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P. KT Water Resource L. P. [Member] KT Water Resource L. P. 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Cumulative number of shares issued pursuant to the Plan. Business Acquisition, Acquiree [Domain] Business Acquisition, Acquiree [Domain] California franchise tax Deferred Tax Assets, State Taxes Granted (in dollars per share) Share-based Compensation Arrangement by Share-based Payment Award, Non-Option Equity Instruments, Granted, Weighted Average Grant Date Fair Value Share-based Compensation Arrangement by Share-based Payment Award, Non-Option Equity Instruments, Granted, Weighted Average Grant Date Fair Value Less: Segment Reconciliation [Abstract] Supplemental disclosure of non-cash activities: Supplemental disclosure of non-cash activities: Cash Flow, Noncash Investing and Financing Activities Disclosure [Abstract] Geographical [Axis] Geographical [Axis] Recoveries of accounts written off SEC Schedule, 12-09, Valuation Allowances and Reserves, Addition, Recovery Aggregate Grant Date Fair Value of Equity Award Amounts Reported in Summary Compensation Table Aggregate Grant Date Fair Value of Equity Award Amounts Reported in Summary Compensation Table [Member] Other Other Regulatory Assets [Member] Other Regulatory Assets [Member] Employee stock purchase plan (in shares) Stock Issued During Period, Shares, Employee Stock Purchase Plans Cash and cash equivalents, beginning of year Cash and cash equivalents, end of year Cash and cash equivalents Cash, Cash Equivalents, Restricted Cash, and Restricted Cash Equivalents Contributions in aid of construction Contributions in Aid of Construction Income tax temporary differences Future income tax benefits due to customers Deferred Income Tax Charge [Member] Share-based payment arrangement, nonvested award, cost not yet recognized, amount Share-Based Payment Arrangement, Nonvested Award, Cost Not yet Recognized, Amount Current assets: Current assets: Assets, Current [Abstract] Transmission and distribution plant Public Utilities, Property, Plant and Equipment, Transmission and Distribution, Useful Life Consolidation Items [Axis] Consolidation Items [Axis] Indefinite-Lived Intangible Assets, Major Class Name [Domain] Indefinite-Lived Intangible Assets, Major Class Name [Domain] Financial Instruments and Investments Fair Value of Financial Instruments, Policy [Policy Text Block] Agreement to purchase water (in gallons of water) Long-term Purchase Commitment, Water Purchased Long-term Purchase Commitment, Water Purchased Accrued interest, expense net of the benefit of tax deductions Unrecognized Tax Benefits, Interest on Income Taxes Accrued Forgone Recovery due to Disqualification of Tax Benefits, Amount Forgone Recovery due to Disqualification of Tax Benefits, Amount Interest Interest Paid, Including Capitalized Interest, Operating and Investing Activities Allowance for doubtful accounts: SEC Schedule, 12-09, Allowance, Credit Loss [Member] Vested (in dollars per share) Share-Based Compensation Arrangement by Share-Based Payment Award, Equity Instruments Other than Options, Vested in Period, Weighted Average Grant Date Fair Value Preferred stock, shares outstanding (in shares) Preferred Stock, Shares Outstanding Schedule of Real Estate Investments Schedule of Real Estate Investments [Table Text Block] Tabular disclosure of real estate investments. 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Property, Plant and Equipment [Line Items] Public Utility, Property, Plant and Equipment [Line Items] Common stock, shares authorized (in shares) Common Stock, Shares Authorized Plans with accumulated benefit obligation in excess of plan assets: Defined Benefit Plan, Plan with Accumulated Benefit Obligation in Excess of Plan Assets [Abstract] Payments for business acquisitions Payments to Acquire Businesses, Net of Cash Acquired Annual maximum contribution limit under Dependent Care Spending Account plan Dependent Care Spending Account, Annual Maximum Employee Contribution Dependent Care Spending Account, Annual Maximum Employee Contribution Tennessee Properties Tennessee Properties [Member] Tennessee Properties Long-term Debt, Type [Axis] Long-Term Debt, Type [Axis] Weighted- Average Grant- Date Fair Value Share-based Compensation Arrangement by Share-based Payment Award, Non-Option Equity Instruments, Weighted Average Grant Date Fair Value [Roll Forward] [Roll Forward] Share-based Compensation Arrangement by Share-based Payment Award, Non-Option Equity Instruments, Weighted Average Grant Date Fair Value [Roll Forward] [Roll Forward] Business combinations debt premium Business combinations debt premium [Member] Business combinations debt premium Entity Voluntary Filers Entity Voluntary Filers Loss (gain) on sale of nonutility properties and other assets Gain (Loss) on Disposition of Property Plant Equipment, Excluding Oil and Gas Property and Timber Property, And On Sale Of Investment Real Estate Gain (Loss) on Disposition of Property Plant Equipment, Excluding Oil and Gas Property and Timber Property, And On Sale Of Investment Real Estate Related Party Related Party [Member] Equity funds capitalized Equity Funds Capitalized Equity Funds Capitalized Deferred income taxes Deferred income taxes Deferred Income Tax Expense (Benefit) Benefit obligations, discount rate Defined Benefit Plan, Assumptions Used Calculating Benefit Obligation, Discount Rate Other 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SEC Schedule, 12-09, Valuation Allowances and Reserves, Amount Revenue adjustment mechanisms Revenue Adjustment Mechanisms [Member] Revenue adjustment mechanisms Regulatory Asset [Domain] Regulatory Asset [Domain] PEO Name PEO Name TWC TWC, Inc. [Member] TWC, Inc. 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progress Public Utilities, Property, Plant and Equipment, Construction Work in Progress Accumulated Other Comprehensive Income (Loss) AOCI Attributable to Parent [Member] Schedule of Regulatory Assets, Net Schedule of Regulatory Assets [Table Text Block] Statement [Line Items] Statement [Line Items] Wholesale water supply assets Wholesale Water Supply Assets Wholesale Water Supply Assets Less accumulated depreciation and amortization Less: accumulated depreciation and amortization Nonutility Properties And Real Estate Investments, Accumulated Depreciation And Amortization Nonutility Properties And Real Estate Investments, Accumulated Depreciation And Amortization Public Utility, Bonds Public Utility, Bonds [Member] Restricted net assets, subsidiaries Restricted Net Assets, Subsidiaries Restricted Net Assets, Subsidiaries Benefits paid and settlements Defined Benefit Plan, Plan Assets, Benefits Paid Compensation Actually Paid vs. Total Shareholder Return Compensation Actually Paid vs. 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construction, non-refundable Customer Advances for Construction, Non-Refundable Customer Advances for Construction, Non-Refundable Lines of credit Line of credit Line of Credit, Current Business Segments [Axis] Segments [Axis] Change in Fair Value as of Vesting Date of Prior Year Equity Awards Vested in Covered Year Change in Fair Value as of Vesting Date of Prior Year Equity Awards Vested in Covered Year [Member] MDC The Metropolitan District [Member] The Metropolitan District [Member] Exercise Price Award Exercise Price Schedule of Deferred Tax Assets and Liabilities Schedule of Deferred Tax Assets and Liabilities [Table Text Block] Health care cost trend rate assumed, next fiscal year Defined Benefit Plan, Health Care Cost Trend Rate Assumed, Next Fiscal Year Cost to retire utility plant, net of salvage Payments for (Proceeds from) Removal Costs Arrangement Duration Trading Arrangement Duration Source of supply Public Utilities, Property, Plant and Equipment, Source of Supply Public Utilities, Property, Plant and Equipment, Source of Supply Schedule of Asset Retirement Obligations Schedule of Asset Retirement Obligations [Table Text Block] Operating loss carryforwards Operating Loss Carryforwards Subsidiaries Subsidiaries [Member] Investments Investments Material Terms of Trading Arrangement Material Terms of Trading Arrangement [Text Block] 2028 Finite-Lived Intangible Asset, Expected Amortization, Year Four Discount rate Asset Retirement Obligation, Discount Rate Asset Retirement Obligation, Discount Rate All Individuals All Individuals [Member] Number of people served from acquisition Public Utilities, Acquisition, Number of People Served Public Utilities, Acquisition, Number of People Served Income Tax Disclosure [Abstract] Income Tax Disclosure [Abstract] Other, net Other, net Other Nonoperating Income (Expense) Long-term purchase commitment, wholesale discount (in USD per hundred cubic feet) Long-term Purchase Commitment, Wholesale Discount Long-term Purchase Commitment, Wholesale Discount Proceeds receivable from sale of real estate investments Proceeds Receivable From Sale Of Real Estate Investments Proceeds Receivable From Sale Of Real Estate Investments Other Postretirement Benefits Other Postretirement Benefits Plan [Member] Market-based RSU Market-based RSU [Member] Market-based RSU [Member] Utility plant net intangible assets Intangible Assets, Net (Excluding Goodwill) Statement of Stockholders' Equity [Abstract] Statement of Stockholders' Equity [Abstract] Retirement obligation, present value Asset Retirement Obligation, Legally Restricted Assets, Fair Value Granted (in shares) Share-Based Compensation Arrangement by Share-Based Payment Award, Non-Option Equity Instruments, Granted ESPP proceeds Proceeds, Issuance of Shares, Share-Based Payment Arrangement, Including Option Exercised Santa Clara Valley Water District Santa Clara Valley Water District [Member] Santa Clara Valley Water District [Member] Schedule of Line of Credit Facilities Schedule of Line of Credit Facilities [Table Text Block] Asset acquisition, consideration transferred before transaction costs Asset Acquisition, Consideration Transferred Before Transaction Costs Asset Acquisition, Consideration Transferred Before Transaction Costs Change in plan assets Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward] Business Combination, Asset Acquisition, and Joint Venture Formation [Abstract] Contributions in aid of construction Payments to Acquire Water Systems using Contributions In Aid of Construction Payments to Acquire Water Systems using Contributions In Aid of Construction Current liabilities Liability, Defined Benefit Plan, Current Related and Nonrelated Parties [Domain] Related and Nonrelated Parties [Domain] Contract agreement, term Contract Agreement, Term Contract Agreement, Term Annual maximum contribution limit under Health Care Spending Account plan Health Care Spending Account, Annual Maximum Employee 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Equity Instruments, Vested, Number Reduction in delivery schedule, percent Reduction in Delivery Schedule, Percent Reduction in Delivery Schedule, Percent Finite-Lived Intangible Assets [Line Items] Finite-Lived Intangible Assets [Line Items] Other Deferred Tax Assets, Other Financing activities: Financing activities: Net Cash Provided by (Used in) Financing Activities [Abstract] 2029 Defined Benefit Plan, Expected Future Benefit Payment, Year Five Borrowings from subsidiaries for notes payable Proceed From Subsidiary Notes Payable Proceed From Subsidiary Notes Payable State taxes, net of federal income tax benefit Effective Income Tax Rate Reconciliation, State and Local Income Taxes, Amount Regulatory Liabilities Regulatory Liability Total deferred tax liabilities Deferred Tax Liabilities, Gross CTWS Credit Agreement Maturing August 2028 CTWS Syndicated Credit Agreement Maturing August 2028 [Member] CTWS Syndicated Credit Agreement Maturing August 2028 —Basic (in dollars per share) 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[Member] Connecticut Water Service, Inc. [Member] Schedule of Net Funded Status Schedule of Net Funded Status [Table Text Block] Actuarial gain (loss), data and other changes Defined Benefit Plan Actuarial Gain (Loss), Data And Other Changes Defined Benefit Plan Actuarial Gain (Loss), Data And Other Changes KT Water Development Ltd KT Water Development Ltd [Member] KT Water Development Ltd Nonvested, beginning balance (in shares) Nonvested, ending balance (in shares) Share-Based Compensation Arrangement by Share-Based Payment Award, Equity Instruments Other than Options, Nonvested, Number Insider Trading Arrangements [Line Items] Fair value of restricted stock awards Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Vested, Grant Date Fair Value Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Vested, Grant Date Fair Value Other Services Segment Reporting, Reconciling Item, Excluding Corporate Nonsegment [Member] Components of Real Estate Investments [Abstract] Real Estate [Abstract] Defined benefit plan, accumulated benefit obligation Defined Benefit Plan, Accumulated Benefit Obligation Forfeited (in shares) Share-Based Compensation Arrangement by Share-Based Payment Award, Non-Option Equity Instruments, Forfeitures and Expirations Authorized revenue, threshold percentage Regulatory Balancing And Memorandum Accounts Review, Authorized Revenue, Threshold Percentage Threshold balance of regulatory balancing or memorandum accounts as a percentage of authorized revenue to trigger an account review. 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