2.2.0.7 true Consolidated Statements of Cash Flows (USD $) 0130 - Statement - Consolidated Statements of Cash Flows true false In Thousands false false 1 USD false false USD Standard http://www.xbrl.org/2003/iso4217 USD iso4217 0 USDEPS Divide http://www.xbrl.org/2003/iso4217 USD iso4217 http://www.xbrl.org/2003/instance shares xbrli 0 Shares Standard http://www.xbrl.org/2003/instance shares xbrli 0 Pure Standard http://www.xbrl.org/2003/instance pure xbrli 0 $ false 2 USD false false USD Standard http://www.xbrl.org/2003/iso4217 USD iso4217 0 USDEPS Divide http://www.xbrl.org/2003/iso4217 USD iso4217 http://www.xbrl.org/2003/instance shares xbrli 0 Shares Standard http://www.xbrl.org/2003/instance shares xbrli 0 Pure Standard http://www.xbrl.org/2003/instance pure xbrli 0 $ false 3 USD false false USD Standard http://www.xbrl.org/2003/iso4217 USD iso4217 0 USDEPS Divide http://www.xbrl.org/2003/iso4217 USD iso4217 http://www.xbrl.org/2003/instance shares xbrli 0 Shares Standard http://www.xbrl.org/2003/instance shares xbrli 0 $ 2 OPERATING ACTIVITIES 2 us-gaap_NetCashProvidedByUsedInOperatingActivitiesAbstract us-gaap true na duration No definition available. false false false false false true false false false false false verboselabel false 1 false false false false 0 0 false false false 2 false false false false 0 0 false false false 3 false false false false 0 0 false false false xbrli:stringItemType string The net cash from (used in) all of the entity's operating activities, including those of discontinued operations, of the reporting entity. Operating activities include all transactions and events that are not defined as investing or financing activities. Operating activities generally involve producing and delivering goods and providing services. Cash flows from operating activities are generally the cash effects of transactions and other events that enter into the determination of net income. false 3 Net income 2 us-gaap_NetIncomeLoss us-gaap true credit duration No definition available. false false false false false false false false false false false verboselabel false 1 true true false false 111205000 111205 false false false 2 true true false false 121693000 121693 false false false 3 true true false false 117843000 117843 false false false xbrli:monetaryItemType monetary The portion of consolidated profit or loss for the period, net of income taxes, which is attributable to the parent. If the entity does not present consolidated financial statements, the amount of profit or loss for the period, net of income taxes. Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 03 -Paragraph 19 -Article 5 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher AICPA -Name Accounting Research Bulletin (ARB) -Number 51 -Paragraph 38 -Subparagraph d Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher AICPA -Name Accounting Research Bulletin (ARB) -Number 51 -Paragraph A7 -Appendix A Reference 4: http://www.xbrl.org/2003/role/presentationRef -Publisher AICPA -Name Accounting Research Bulletin (ARB) -Number 51 -Paragraph 38 -Subparagraph a Reference 5: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 04 -Paragraph 20 -Article 9 Reference 6: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 130 -Paragraph 10, 15 Reference 7: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Emerging Issues Task Force (EITF) -Number 87-21 Reference 8: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 95 -Paragraph 28, 29, 30 false 4 ADJUSTMENTS TO RECONCILE NET INCOME TO NET CASH PROVIDED BY OPERATING ACTIVITIES 2 us-gaap_AdjustmentsToReconcileNetIncomeLossToCashProvidedByUsedInOperatingActivitiesAbstract us-gaap true na duration No definition available. false false false false false true false false false false false verboselabel false 1 false false false false 0 0 false false false 2 false false false false 0 0 false false false 3 false false false false 0 0 false false false xbrli:stringItemType string No definition available. false 5 Depreciation and amortization 2 us-gaap_UtilitiesOperatingExpenseDepreciationAndAmortization us-gaap true debit duration No definition available. false false false false false false false false false false false verboselabel false 1 false true false false 94011000 94011 false false false 2 false true false false 95357000 95357 false false false 3 false true false false 95007000 95007 false false false xbrli:monetaryItemType monetary Discloses the amount of operating expense for the period related to depreciation and amortization. No authoritative reference available. false 6 Amortization of: 2 us-gaap_AdjustmentForAmortizationAbstract us-gaap true na duration No definition available. false false false false false true false false false false false verboselabel false 1 false false false false 0 0 false false false 2 false false false false 0 0 false false false 3 false false false false 0 0 false false false xbrli:stringItemType string No definition available. false 7 Other regulatory assets and liabilities-net 2 wgl_OtherRegulatoryAssetsAndLiabilitiesNet wgl false debit duration Other regulatory assets and liabilities net. false false false false false false false false false false false verboselabel false 1 false true false false 3686000 3686 false false false 2 false true false false 3350000 3350 false false false 3 false true false false 2666000 2666 false false false xbrli:monetaryItemType monetary Other regulatory assets and liabilities net. No authoritative reference available. false 8 Debt related costs 2 us-gaap_AmortizationOfFinancingCostsAndDiscounts us-gaap true debit duration No definition available. false false false false false false false false false false false verboselabel false 1 false true false false 767000 767 false false false 2 false true false false 785000 785 false false false 3 false true false false 925000 925 false false false xbrli:monetaryItemType monetary The component of interest expense representing the noncash expenses charged against earnings in the period to allocate debt discount and premium, and the costs to issue debt and obtain financing over the related debt instruments. Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 95 -Paragraph 28 false 9 Deferred income taxes-net 2 us-gaap_DeferredIncomeTaxExpenseBenefit us-gaap true debit duration No definition available. false false false false false false false false false false false verboselabel false 1 false true false false 102897000 102897 false false false 2 false true false false 67401000 67401 false false false 3 false true false false 5863000 5863 false false false xbrli:monetaryItemType monetary The component of income tax expense for the period representing the net change in the entity's deferred tax assets and liabilities pertaining to continuing operations. Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Staff Accounting Bulletin (SAB) -Number Topic 6 -Section I -Subsection 7 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 109 -Paragraph 45 -Subparagraph b Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 95 -Paragraph 28 Reference 4: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 109 -Paragraph 289 Reference 5: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 08 -Paragraph h -Article 4 false 10 Accrued/deferred pension cost 2 wgl_AccruedDeferredPensionCost wgl false debit duration Accrued/deferred pension cost. false false false false false false false false false false false verboselabel false 1 false true false false 9648000 9648 false false false 2 false true false false -2204000 -2204 false false false 3 false true false false -4219000 -4219 false false false xbrli:monetaryItemType monetary Accrued/deferred pension cost. No authoritative reference available. false 11 Compensation expense related to equity awards 2 us-gaap_ShareBasedCompensation us-gaap true debit duration No definition available. false false false false false false false false false false false verboselabel false 1 false true false false 2492000 2492 false false false 2 false true false false 2160000 2160 false false false 3 false true false false 4111000 4111 false false false xbrli:monetaryItemType monetary The aggregate amount of noncash, equity-based employee remuneration. This may include the value of stock options, amortization of restricted stock, and adjustment for officers compensation. As noncash, this element is an add back when calculating net cash generated by operating activities using the indirect method. Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 95 -Paragraph 28 false 12 Provision for doubtful accounts 2 us-gaap_ProvisionForDoubtfulAccounts us-gaap true debit duration No definition available. false false false false false false false false false false false verboselabel false 1 false true false false 17766000 17766 false false false 2 false true false false 22435000 22435 false false false 3 false true false false 19958000 19958 false false false xbrli:monetaryItemType monetary Amount of the current period expense charged against operations, the offset which is generally to the allowance for doubtful accounts for the purpose of reducing receivables, including notes receivable, to an amount that approximates their net realizable value (the amount expected to be collected). Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 95 -Paragraph 28 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 03 -Paragraph 5 -Article 5 false 13 Other non-cash credits-net 2 us-gaap_AdjustmentsNoncashItemsToReconcileNetIncomeLossToCashProvidedByUsedInOperatingActivitiesOther us-gaap true debit duration No definition available. false false false false false false false false false false false verboselabel false 1 false true false false -415000 -415 false false false 2 false true false false -125000 -125 false false false 3 false true false false -1894000 -1894 false false false xbrli:monetaryItemType monetary Transactions that do not result in cash inflows or outflows in the period in which they occur, but affect net income and thus are removed when calculating net cash flow from operating activities using the indirect cash flow method. This element is used when there is not a more specific and appropriate element. Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 95 -Paragraph 28 false 14 CHANGES IN ASSETS AND LIABILITIES 2 us-gaap_IncreaseDecreaseInOperatingCapitalAbstract us-gaap true na duration No definition available. false false false false false true false false false false false verboselabel false 1 false false false false 0 0 false false false 2 false false false false 0 0 false false false 3 false false false false 0 0 false false false xbrli:stringItemType string No definition available. false 15 Accounts receivable and unbilled revenues 2 us-gaap_IncreaseDecreaseInAccountsAndOtherReceivables us-gaap true credit duration No definition available. false false false false false false false false false false true negated false 1 false true false false -65522000 -65522 false false false 2 false true false false -30555000 -30555 false false false 3 false true false false -65019000 -65019 false false false xbrli:monetaryItemType monetary The net change during the reporting period in the amount due from customers for the credit sale of goods and services; includes accounts receivable and other types of receivables. Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 95 -Paragraph 28 false 16 Gas costs and other regulatory assets/liabilities-net 2 us-gaap_IncreaseDecreaseInRegulatoryAssetsAndLiabilities us-gaap true credit duration No definition available. false false false false false false false false false false true negated false 1 false true false false 53510000 53510 false false false 2 false true false false -47968000 -47968 false false false 3 false true false false -19093000 -19093 false false false xbrli:monetaryItemType monetary The net change during the reporting period in the value of assets that are created when regulatory agencies permits public utilities to defer costs (revenues) to the balance sheet. This element is a the net change of regulatory assets and liabilities combined. No authoritative reference available. false 17 Storage gas 2 us-gaap_IncreaseDecreaseInInventories us-gaap true credit duration No definition available. false false false false false false false false false false true negated false 1 false true false false -4542000 -4542 false false false 2 false true false false 168948000 168948 false false false 3 false true false false -111740000 -111740 false false false xbrli:monetaryItemType monetary The net change during the reporting period in the aggregate value of all inventory held by the reporting entity, associated with underlying transactions that are classified as operating activities. Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 95 -Paragraph 28 false 18 Other prepayments 2 us-gaap_IncreaseDecreaseInPrepaidExpense us-gaap true credit duration No definition available. false false false false false false false false false false true negated false 1 false true false false -10138000 -10138 false false false 2 false true false false -52513000 -52513 false false false 3 false true false false -4379000 -4379 false false false xbrli:monetaryItemType monetary The net change during the reporting period in the amount of outstanding money paid in advance for goods or services that bring economic benefits for future periods. Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 95 -Paragraph 28 false 19 Accounts payable and other accrued liabilities 2 us-gaap_IncreaseDecreaseInAccountsPayableAndAccruedLiabilities us-gaap true debit duration No definition available. false false false false false false false false false false false verboselabel false 1 false true false false 8905000 8905 false false false 2 false true false false -34505000 -34505 false false false 3 false true false false 33479000 33479 false false false xbrli:monetaryItemType monetary The net change during the reporting period in the aggregate amount of obligations and expenses incurred but not paid. Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 95 -Paragraph 28 false 20 Wages payable 2 us-gaap_IncreaseDecreaseInAccruedSalaries us-gaap true debit duration No definition available. false false false false false false false false false false false verboselabel false 1 false true false false 1117000 1117 false false false 2 false true false false 1188000 1188 false false false 3 false true false false 629000 629 false false false xbrli:monetaryItemType monetary Net change during the period in the amount of salaries accrued at the period end. Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 95 -Paragraph 28 false 21 Customer deposits and advance payments 2 wgl_CustomerDepositsAndAdvancePayments wgl false debit duration Customer deposits and advance payments false false false false false false false false false false false verboselabel false 1 false true false false 12435000 12435 false false false 2 false true false false 6834000 6834 false false false 3 false true false false -3172000 -3172 false false false xbrli:monetaryItemType monetary Customer deposits and advance payments No authoritative reference available. false 22 Accrued taxes 2 us-gaap_IncreaseDecreaseInAccruedIncomeTaxesPayable us-gaap true debit duration No definition available. false false false false false false false false false false false verboselabel false 1 false true false false -2291000 -2291 false false false 2 false true false false 4990000 4990 false false false 3 false true false false 356000 356 false false false xbrli:monetaryItemType monetary The net change during the period in the amount of cash payments due to taxing authorities for taxes that are based on the reporting entity's earnings. Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 95 -Paragraph 28 false 23 Accrued interest 2 us-gaap_IncreaseDecreaseInInterestPayableNet us-gaap true debit duration No definition available. false false false false false false false false false false false verboselabel false 1 false true false false 385000 385 false false false 2 false true false false -602000 -602 false false false 3 false true false false -16000 -16 false false false xbrli:monetaryItemType monetary The net change during the reporting period in interest payable, which represents the amount owed to note holders, bond holders, and other parties for interest earned on loans or credit extended to the reporting entity. Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 95 -Paragraph 28 false 24 Other current assets 2 us-gaap_IncreaseDecreaseInOtherOperatingAssets us-gaap true credit duration No definition available. false false false false false false false false false false true negated false 1 false true false false -4815000 -4815 false false false 2 false true false false -7173000 -7173 false false false 3 false true false false 350000 350 false false false xbrli:monetaryItemType monetary The net change during the reporting period in other operating assets not otherwise defined in the taxonomy. Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 95 -Paragraph 28 false 25 Other current liabilities 2 us-gaap_IncreaseDecreaseInOtherOperatingLiabilities us-gaap true debit duration No definition available. false false false false false false false false false false false verboselabel false 1 false true false false 31142000 31142 false false false 2 false true false false -24678000 -24678 false false false 3 false true false false 28498000 28498 false false false xbrli:monetaryItemType monetary The net change during the reporting period in other operating obligations not otherwise defined in the taxonomy. Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 95 -Paragraph 28 false 26 Deferred gas costs-net 2 us-gaap_IncreaseDecreaseInDeferredGasCost us-gaap true credit duration No definition available. false false false false false false false false false false true negated false 1 false true false false 8005000 8005 false false false 2 false true false false 36801000 36801 false false false 3 false true false false -24556000 -24556 false false false xbrli:monetaryItemType monetary The net change during the reporting period in carrying amount of capitalized gas costs of a regulated entity that are expected to be recoverable through rate adjustments within one year or the normal operating cycle, if longer. Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 95 -Paragraph 28 false 27 Deferred assets-other 2 us-gaap_IncreaseDecreaseInDeferredCharges us-gaap true credit duration No definition available. false false false false false false false false false false true negated false 1 false true false false -51119000 -51119 false false false 2 false true false false -18662000 -18662 false false false 3 false true false false -10808000 -10808 false false false xbrli:monetaryItemType monetary The net change during the reporting period in the value of expenditures made during the current reporting period for benefits that will be received over a period of years. Deferred charges differ from prepaid expenses in that they usually extend over a long period of time and may or may not be regularly recurring costs of operation. Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 95 -Paragraph 28 false 28 Deferred liabilities-other 2 us-gaap_IncreaseDecreaseInOtherDeferredLiability us-gaap true debit duration No definition available. false false false false false false false false false false false verboselabel false 1 false true false false -27698000 -27698 false false false 2 false true false false -7466000 -7466 false false false 3 false true false false -2385000 -2385 false false false xbrli:monetaryItemType monetary The net change during the reporting period in other obligations not otherwise defined in the taxonomy where the payments will be made in future periods. Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 95 -Paragraph 28 false 29 Other-net 2 us-gaap_IncreaseDecreaseInOtherOperatingCapitalNet us-gaap true credit duration No definition available. false false false false false false false false false false true negatedtotal false 1 false true false false -459000 -459 false false false 2 false true false false 2916000 2916 false false false 3 false true false false 878000 878 false false false xbrli:monetaryItemType monetary For entities with classified balance sheets, the net change during the reporting period in the value of other assets or liabilities used in operating activities, that are not otherwise defined in the taxonomy. For entities with unclassified balance sheets, the net change during the reporting period in the value of all other assets or liabilities used in operating activities. Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 95 -Paragraph 28 true 30 Net Cash Provided by Operating Activities 2 us-gaap_NetCashProvidedByUsedInOperatingActivities us-gaap true na duration No definition available. false false false false false false false false false false false totallabel false 1 false true false false 290972000 290972 false false false 2 false true false false 308407000 308407 false false false 3 false true false false 63282000 63282 false false false xbrli:monetaryItemType monetary The net cash from (used in) all of the entity's operating activities, including those of discontinued operations, of the reporting entity. Operating activities generally involve producing and delivering goods and providing services. Operating activity cash flows include transactions, adjustments, and changes in value that are not defined as investing or financing activities. Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 95 -Paragraph 28 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 95 -Paragraph 26 true 31 FINANCING ACTIVITIES 2 us-gaap_NetCashProvidedByUsedInFinancingActivitiesAbstract us-gaap true na duration No definition available. false false false false false true false false false false false verboselabel false 1 false false false false 0 0 false false false 2 false false false false 0 0 false false false 3 false false false false 0 0 false false false xbrli:stringItemType string No definition available. false 32 Common stock issued 2 us-gaap_ProceedsFromIssuanceOfCommonStock us-gaap true debit duration No definition available. false false false false false false false false false false false verboselabel false 1 false true false false 22150000 22150 false false false 2 false true false false 5131000 5131 false false false 3 false true false false 14064000 14064 false false false xbrli:monetaryItemType monetary The cash inflow from the additional capital contribution to the entity. Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 95 -Paragraph 18 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 95 -Paragraph 19 -Subparagraph a false 33 Long-term debt issued 2 us-gaap_ProceedsFromIssuanceOfLongTermDebt us-gaap true debit duration No definition available. false false false false false false false false false false false verboselabel false 1 false true false false 53018000 53018 false false false 2 false true false false 64875000 64875 false false false 3 false true false false 63285000 63285 false false false xbrli:monetaryItemType monetary The cash inflow from a debt initially having maturity due after one year or beyond the operating cycle, if longer. Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 95 -Paragraph 18 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 95 -Paragraph 19 -Subparagraph b false 34 Long-term debt retired 2 us-gaap_RepaymentsOfLongTermDebt us-gaap true credit duration No definition available. false false false false false false false false false false true negated false 1 false true false false -74019000 -74019 false false false 2 false true false false -76012000 -76012 false false false 3 false true false false -21110000 -21110 false false false xbrli:monetaryItemType monetary The cash outflow for debt initially having maturity due after one year or beyond the normal operating cycle, if longer. Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 95 -Paragraph 18 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 95 -Paragraph 20 -Subparagraph b false 35 Debt issuance costs 2 us-gaap_PaymentsOfDebtIssuanceCosts us-gaap true credit duration No definition available. false false false false false false false false false false true negated false 1 false true false false -335000 -335 false false false 2 false true false false -181000 -181 false false false 3 false false false false 0 0 false false false xbrli:monetaryItemType monetary The cash outflow paid to third parties in connection with debt origination, which will be amortized over the remaining maturity period of the associated long-term debt. Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Emerging Issues Task Force (EITF) -Number 95-13 false 36 Notes payable issued (retired)-net 2 us-gaap_ProceedsFromRepaymentsOfShortTermDebt us-gaap true debit duration No definition available. false false false false false false false false false false false verboselabel false 1 false true false false -83434000 -83434 false false false 2 false true false false -87104000 -87104 false false false 3 false true false false 86708000 86708 false false false xbrli:monetaryItemType monetary The net cash inflow (outflow) for borrowing having initial term of repayment within one year or the normal operating cycle, if longer. Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 95 -Paragraph 18 false 37 Dividends on common stock and preferred stock 2 us-gaap_PaymentsOfOrdinaryDividends us-gaap true credit duration No definition available. false false false false false false false false false false true negated false 1 false true false false -76525000 -76525 false false false 2 false true false false -73707000 -73707 false false false 3 false true false false -70456000 -70456 false false false xbrli:monetaryItemType monetary The cash outflow from distribution of an entity's earnings to common and preferred stockholders, including minority shareholders. This element excludes special dividends, which are included in a separate element for capital distributions. Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 95 -Paragraph 18 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 95 -Paragraph 20 -Subparagraph a false 38 Other financing activities-net 2 us-gaap_ProceedsFromPaymentsForOtherFinancingActivities us-gaap true debit duration No definition available. false false false false false false false false false false false totallabel false 1 false true false false -717000 -717 false false false 2 false true false false -820000 -820 false false false 3 false true false false 482000 482 false false false xbrli:monetaryItemType monetary The net cash inflow (outflow) from other financing activities. This element is used when there is not a more specific and appropriate element in the taxonomy. Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 95 -Paragraph 18, 19, 20 true 39 Net Cash Provided by (Used in) Financing Activities 2 us-gaap_NetCashProvidedByUsedInFinancingActivities us-gaap true debit duration No definition available. false false false false false false false false false false false totallabel false 1 false true false false -159862000 -159862 false false false 2 false true false false -167818000 -167818 false false false 3 false true false false 72973000 72973 false false false xbrli:monetaryItemType monetary The net cash inflow (outflow) from financing activity for the period. Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 95 -Paragraph 26 true 40 INVESTING ACTIVITIES 2 us-gaap_NetCashProvidedByUsedInInvestingActivitiesAbstract us-gaap true na duration No definition available. false false false false false true false false false false false verboselabel false 1 false false false false 0 0 false false false 2 false false false false 0 0 false false false 3 false false false false 0 0 false false false xbrli:stringItemType string No definition available. false 41 Capital expenditures (excluding Allowance for Funds Used During Construction) 2 us-gaap_PaymentsToAcquireProductiveAssets us-gaap true credit duration No definition available. false false false false false false false false false false true negatedtotal false 1 false true false false -130106000 -130106 false false false 2 false true false false -138908000 -138908 false false false 3 false true false false -134961000 -134961 false false false xbrli:monetaryItemType monetary The cash outflow for purchases of and capital improvements on property, plant and equipment (capital expenditures), software, and other intangible assets. Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 95 -Paragraph 15 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 95 -Paragraph 17 -Subparagraph c true 42 Net Cash Used in Investing Activities 2 us-gaap_NetCashProvidedByUsedInInvestingActivities us-gaap true debit duration No definition available. false false false false false false false false false false false totallabel false 1 false true false false -130106000 -130106 false false false 2 false true false false -138908000 -138908 false false false 3 false true false false -134961000 -134961 false false false xbrli:monetaryItemType monetary The net cash inflow (outflow) from investing activity. Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 95 -Paragraph 26 true 43 INCREASE IN CASH AND CASH EQUIVALENTS 2 us-gaap_CashAndCashEquivalentsPeriodIncreaseDecrease us-gaap true na duration No definition available. false false false false false false false false false false false verboselabel false 1 false true false false 1004000 1004 false false false 2 false true false false 1681000 1681 false false false 3 false true false false 1294000 1294 false false false xbrli:monetaryItemType monetary The net change between the beginning and ending balance of cash and cash equivalents. Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 95 -Paragraph 26 false 44 Cash and Cash Equivalents at Beginning of Year 2 us-gaap_CashAndCashEquivalentsAtCarryingValue us-gaap true debit instant No definition available. false false false false false false false false true false false periodstartlabel false 1 false true false false 7845000 7845 false false false 2 false true false false 6164000 6164 false false false 3 false true false false 4870000 4870 false false false xbrli:monetaryItemType monetary Includes currency on hand as well as demand deposits with banks or financial institutions. It also includes other kinds of accounts that have the general characteristics of demand deposits in that the Entity may deposit additional funds at any time and also effectively may withdraw funds at any time without prior notice or penalty. Cash equivalents, excluding items classified as marketable securities, include short-term, highly liquid investments that are both readily convertible to known amounts of cash, and so near their maturity that they present minimal risk of changes in value because of changes in interest rates. Generally, only investments with original maturities of three months or less qualify under that definition. Original maturity means original maturity to the entity holding the investment. For example, both a three-month US Treasury bill and a three-year Treasury note purchased three months from maturity qualify as cash equivalents. However, a Treasury note purchased three years ago does not become a cash equivalent when its remaining maturity is three months. Compensating balance arrangements that do not legally restrict the withdrawal or usage of cash amounts may be reported as Cash and Cash Equivalents, while legally restricted deposits held as compensating balances against borrowing arrangements, contracts entered into with others, or company statements of intention with regard to particular deposits should not be reported as cash and cash equivalents. Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 95 -Paragraph 7, 26 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 95 -Paragraph 8, 9 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 95 -Paragraph 7 -Footnote 1 Reference 4: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 02 -Paragraph 1 -Article 5 false 45 Cash and Cash Equivalents at End of Year 2 us-gaap_CashAndCashEquivalentsAtCarryingValue us-gaap true debit instant No definition available. false false false false false false false false false true false periodendlabel false 1 false true false false 8849000 8849 false false false 2 false true false false 7845000 7845 false false false 3 false true false false 6164000 6164 false false false xbrli:monetaryItemType monetary Includes currency on hand as well as demand deposits with banks or financial institutions. It also includes other kinds of accounts that have the general characteristics of demand deposits in that the Entity may deposit additional funds at any time and also effectively may withdraw funds at any time without prior notice or penalty. Cash equivalents, excluding items classified as marketable securities, include short-term, highly liquid investments that are both readily convertible to known amounts of cash, and so near their maturity that they present minimal risk of changes in value because of changes in interest rates. Generally, only investments with original maturities of three months or less qualify under that definition. Original maturity means original maturity to the entity holding the investment. For example, both a three-month US Treasury bill and a three-year Treasury note purchased three months from maturity qualify as cash equivalents. However, a Treasury note purchased three years ago does not become a cash equivalent when its remaining maturity is three months. Compensating balance arrangements that do not legally restrict the withdrawal or usage of cash amounts may be reported as Cash and Cash Equivalents, while legally restricted deposits held as compensating balances against borrowing arrangements, contracts entered into with others, or company statements of intention with regard to particular deposits should not be reported as cash and cash equivalents. Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 95 -Paragraph 7, 26 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 95 -Paragraph 8, 9 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 95 -Paragraph 7 -Footnote 1 Reference 4: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 02 -Paragraph 1 -Article 5 false 46 SUPPLEMENTAL DISCLOSURES OF CASH FLOW INFORMATION 2 us-gaap_SupplementalCashFlowInformationAbstract us-gaap true na duration No definition available. false false false false false true false false false false false verboselabel false 1 false false false false 0 0 false false false 2 false false false false 0 0 false false false 3 false false false false 0 0 false false false xbrli:stringItemType string No definition available. false 47 Income taxes paid - net 2 us-gaap_IncomeTaxesPaid us-gaap true credit duration No definition available. false false false false false false false false false false false verboselabel false 1 false true false false -78177000 -78177 false false false 2 false true false false 41294000 41294 false false false 3 false true false false 67086000 67086 false false false xbrli:monetaryItemType monetary The amount of cash paid during the current period to foreign, federal, state, and local authorities as taxes on income. Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 95 -Paragraph 29 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 95 -Paragraph 27 -Subparagraph f false 48 Interest paid 2 us-gaap_InterestPaid us-gaap true credit duration No definition available. false false false false false false false false false false false verboselabel false 1 false true false false 39129000 39129 false false false 2 false true false false 44378000 44378 false false false 3 false true false false 46850000 46850 false false false xbrli:monetaryItemType monetary The amount of cash paid during the current period for interest owed on money borrowed; includes amount of interest capitalized Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 95 -Paragraph 29 false 49 SUPPLEMENTAL DISCLOSURES OF NON-CASH INVESTING AND FINANCING ACTIVITIES 2 us-gaap_CashFlowNoncashInvestingAndFinancingActivitiesDisclosureAbstract us-gaap true na duration No definition available. false false false false false true false false false false false verboselabel false 1 false false false false 0 0 false false false 2 false false false false 0 0 false false false 3 false false false false 0 0 false false false xbrli:stringItemType string Designated to encapsulate the entire footnote disclosure that gives information on the supplemental cash flow activities for noncash (or part noncash) transactions for the period. Noncash is defined as information about all investing and financing activities of an enterprise during a period that affect recognized assets or liabilities but that do not result in cash receipts or cash payments in the period. "Part noncash" refers to that portion of the transaction not resulting in cash receipts or cash payments in the period. false 50 Retirement of debt related to project financing 2 us-gaap_ExtinguishmentOfDebtAmount us-gaap true debit duration No definition available. false false false false false false false false false false false verboselabel false 1 false true false false 359000 359 false false false 2 false true false false 24494000 24494 false false false 3 false false false false 0 0 false false false xbrli:monetaryItemType monetary Gross amount of debt extinguished. No authoritative reference available. false 51 Capital expenditures included in accounts payable and other accrued liabilities 2 us-gaap_CapitalExpendituresIncurredButNotYetPaid us-gaap true credit duration No definition available. false false false false false false false false false false false verboselabel false 1 false true false false 7875000 7875 false false false 2 false true false false 3791000 3791 false false false 3 false true false false 7217000 7217 false false false xbrli:monetaryItemType monetary Future cash outflow to pay for purchases of fixed assets that have occurred. No authoritative reference available. false 52 Washington Gas Light Company 0 na true na na No definition available. false true false false false false false false false false false http://wglholdings.com/role/statementsofcashflows false 1 false false false false 0 0 false false false 2 false false false false 0 0 false false false 3 false false false false 0 0 false false false false 4 USD true false false false Washington Gas Light Company dei_LegalEntityAxis xbrldi http://xbrl.org/2006/xbrldi us-gaap_SubsidiariesMember dei_LegalEntityAxis explicitMember USD Standard http://www.xbrl.org/2003/iso4217 USD iso4217 0 Shares Standard http://www.xbrl.org/2003/instance shares xbrli 0 Pure Standard http://www.xbrl.org/2003/instance pure xbrli 0 $ false 5 USD true false false false Washington Gas Light Company dei_LegalEntityAxis xbrldi http://xbrl.org/2006/xbrldi us-gaap_SubsidiariesMember dei_LegalEntityAxis explicitMember USD Standard http://www.xbrl.org/2003/iso4217 USD iso4217 0 Shares Standard http://www.xbrl.org/2003/instance shares xbrli 0 Pure Standard http://www.xbrl.org/2003/instance pure xbrli 0 $ false 6 USD true false false false Washington Gas Light Company dei_LegalEntityAxis xbrldi http://xbrl.org/2006/xbrldi us-gaap_SubsidiariesMember dei_LegalEntityAxis explicitMember USD Standard http://www.xbrl.org/2003/iso4217 USD iso4217 0 $ na No definition available. No authoritative reference available. false 53 OPERATING ACTIVITIES 2 us-gaap_NetCashProvidedByUsedInOperatingActivitiesAbstract us-gaap true na duration No definition available. false false false false false true false false false false false verboselabel false 1 false false false false 0 0 false false false 2 false false false false 0 0 false false false 3 false false false false 0 0 false false false xbrli:stringItemType string The net cash from (used in) all of the entity's operating activities, including those of discontinued operations, of the reporting entity. Operating activities include all transactions and events that are not defined as investing or financing activities. Operating activities generally involve producing and delivering goods and providing services. Cash flows from operating activities are generally the cash effects of transactions and other events that enter into the determination of net income. false 54 Net income 2 us-gaap_NetIncomeLoss us-gaap true credit duration No definition available. false false false false false false false false false false false verboselabel false 1 false true false false 102349000 102349 false false false 2 false true false false 106585000 106585 false false false 3 false true false false 114182000 114182 false false false xbrli:monetaryItemType monetary The portion of consolidated profit or loss for the period, net of income taxes, which is attributable to the parent. If the entity does not present consolidated financial statements, the amount of profit or loss for the period, net of income taxes. Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 03 -Paragraph 19 -Article 5 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher AICPA -Name Accounting Research Bulletin (ARB) -Number 51 -Paragraph 38 -Subparagraph d Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher AICPA -Name Accounting Research Bulletin (ARB) -Number 51 -Paragraph A7 -Appendix A Reference 4: http://www.xbrl.org/2003/role/presentationRef -Publisher AICPA -Name Accounting Research Bulletin (ARB) -Number 51 -Paragraph 38 -Subparagraph a Reference 5: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 04 -Paragraph 20 -Article 9 Reference 6: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 130 -Paragraph 10, 15 Reference 7: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Emerging Issues Task Force (EITF) -Number 87-21 Reference 8: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 95 -Paragraph 28, 29, 30 false 55 ADJUSTMENTS TO RECONCILE NET INCOME TO NET CASH PROVIDED BY OPERATING ACTIVITIES 2 us-gaap_AdjustmentsToReconcileNetIncomeLossToCashProvidedByUsedInOperatingActivitiesAbstract us-gaap true na duration No definition available. false false false false false true false false false false false verboselabel false 1 false false false false 0 0 false false false 2 false false false false 0 0 false false false 3 false false false false 0 0 false false false xbrli:stringItemType string No definition available. false 56 Depreciation and amortization 2 us-gaap_UtilitiesOperatingExpenseDepreciationAndAmortization us-gaap true debit duration No definition available. false false false false false false false false false false false verboselabel false 1 false true false false 92096000 92096 false false false 2 false true false false 93562000 93562 false false false 3 false true false false 93189000 93189 false false false xbrli:monetaryItemType monetary Discloses the amount of operating expense for the period related to depreciation and amortization. No authoritative reference available. false 57 Amortization of: 2 us-gaap_AdjustmentForAmortizationAbstract us-gaap true na duration No definition available. false false false false false true false false false false false verboselabel false 1 false false false false 0 0 false false false 2 false false false false 0 0 false false false 3 false false false false 0 0 false false false xbrli:stringItemType string No definition available. false 58 Other regulatory assets and liabilities-net 2 wgl_OtherRegulatoryAssetsAndLiabilitiesNet wgl false debit duration Other regulatory assets and liabilities net. false false false false false false false false false false false verboselabel false 1 false true false false 3687000 3687 false false false 2 false true false false 3350000 3350 false false false 3 false true false false 2666000 2666 false false false xbrli:monetaryItemType monetary Other regulatory assets and liabilities net. No authoritative reference available. false 59 Debt related costs 2 us-gaap_AmortizationOfFinancingCostsAndDiscounts us-gaap true debit duration No definition available. false false false false false false false false false false false verboselabel false 1 false true false false 767000 767 false false false 2 false true false false 785000 785 false false false 3 false true false false 885000 885 false false false xbrli:monetaryItemType monetary The component of interest expense representing the noncash expenses charged against earnings in the period to allocate debt discount and premium, and the costs to issue debt and obtain financing over the related debt instruments. Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 95 -Paragraph 28 false 60 Deferred income taxes-net 2 us-gaap_DeferredIncomeTaxExpenseBenefit us-gaap true debit duration No definition available. false false false false false false false false false false false verboselabel false 1 false true false false 113382000 113382 false false false 2 false true false false 69009000 69009 false false false 3 false true false false 13559000 13559 false false false xbrli:monetaryItemType monetary The component of income tax expense for the period representing the net change in the entity's deferred tax assets and liabilities pertaining to continuing operations. Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Staff Accounting Bulletin (SAB) -Number Topic 6 -Section I -Subsection 7 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 109 -Paragraph 45 -Subparagraph b Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 95 -Paragraph 28 Reference 4: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 109 -Paragraph 289 Reference 5: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 08 -Paragraph h -Article 4 false 61 Accrued/deferred pension cost 2 wgl_AccruedDeferredPensionCost wgl false debit duration Accrued/deferred pension cost. false false false false false false false false false false false verboselabel false 1 false true false false 9602000 9602 false false false 2 false true false false -2198000 -2198 false false false 3 false true false false -4199000 -4199 false false false xbrli:monetaryItemType monetary Accrued/deferred pension cost. No authoritative reference available. false 62 Compensation expense related to equity awards 2 us-gaap_ShareBasedCompensation us-gaap true debit duration No definition available. false false false false false false false false false false false verboselabel false 1 false true false false 2341000 2341 false false false 2 false true false false 2052000 2052 false false false 3 false true false false 3547000 3547 false false false xbrli:monetaryItemType monetary The aggregate amount of noncash, equity-based employee remuneration. This may include the value of stock options, amortization of restricted stock, and adjustment for officers compensation. As noncash, this element is an add back when calculating net cash generated by operating activities using the indirect method. Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 95 -Paragraph 28 false 63 Provision for doubtful accounts 2 us-gaap_ProvisionForDoubtfulAccounts us-gaap true debit duration No definition available. false false false false false false false false false false false verboselabel false 1 false true false false 13528000 13528 false false false 2 false true false false 18567000 18567 false false false 3 false true false false 16761000 16761 false false false xbrli:monetaryItemType monetary Amount of the current period expense charged against operations, the offset which is generally to the allowance for doubtful accounts for the purpose of reducing receivables, including notes receivable, to an amount that approximates their net realizable value (the amount expected to be collected). Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 95 -Paragraph 28 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 03 -Paragraph 5 -Article 5 false 64 Other non-cash credits-net 2 us-gaap_AdjustmentsNoncashItemsToReconcileNetIncomeLossToCashProvidedByUsedInOperatingActivitiesOther us-gaap true debit duration No definition available. false false false false false false false false false false false verboselabel false 1 false true false false -1107000 -1107 false false false 2 false true false false -419000 -419 false false false 3 false true false false -1892000 -1892 false false false xbrli:monetaryItemType monetary Transactions that do not result in cash inflows or outflows in the period in which they occur, but affect net income and thus are removed when calculating net cash flow from operating activities using the indirect cash flow method. This element is used when there is not a more specific and appropriate element. Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 95 -Paragraph 28 false 65 CHANGES IN ASSETS AND LIABILITIES 2 us-gaap_IncreaseDecreaseInOperatingCapitalAbstract us-gaap true na duration No definition available. false false false false false true false false false false false verboselabel false 1 false false false false 0 0 false false false 2 false false false false 0 0 false false false 3 false false false false 0 0 false false false xbrli:stringItemType string No definition available. false 66 Accounts receivable and unbilled revenues 2 us-gaap_IncreaseDecreaseInAccountsAndOtherReceivables us-gaap true credit duration No definition available. false false false false false false false false false false true negated false 1 false true false false -14503000 -14503 false false false 2 false true false false 10938000 10938 false false false 3 false true false false -66381000 -66381 false false false xbrli:monetaryItemType monetary The net change during the reporting period in the amount due from customers for the credit sale of goods and services; includes accounts receivable and other types of receivables. Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 95 -Paragraph 28 false 67 Gas costs and other regulatory assets/liabilities-net 2 us-gaap_IncreaseDecreaseInRegulatoryAssetsAndLiabilities us-gaap true credit duration No definition available. false false false false false false false false false false true negated false 1 false true false false 53510000 53510 false false false 2 false true false false -47968000 -47968 false false false 3 false true false false -19093000 -19093 false false false xbrli:monetaryItemType monetary The net change during the reporting period in the value of assets that are created when regulatory agencies permits public utilities to defer costs (revenues) to the balance sheet. This element is a the net change of regulatory assets and liabilities combined. No authoritative reference available. false 68 Storage gas 2 us-gaap_IncreaseDecreaseInInventories us-gaap true credit duration No definition available. false false false false false false false false false false true negated false 1 false true false false -467000 -467 false false false 2 false true false false 153817000 153817 false false false 3 false true false false -106846000 -106846 false false false xbrli:monetaryItemType monetary The net change during the reporting period in the aggregate value of all inventory held by the reporting entity, associated with underlying transactions that are classified as operating activities. Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 95 -Paragraph 28 false 69 Other prepayments 2 us-gaap_IncreaseDecreaseInPrepaidExpense us-gaap true credit duration No definition available. false false false false false false false false false false true negated false 1 false true false false -18847000 -18847 false false false 2 false true false false -8070000 -8070 false false false 3 false true false false -5188000 -5188 false false false xbrli:monetaryItemType monetary The net change during the reporting period in the amount of outstanding money paid in advance for goods or services that bring economic benefits for future periods. Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 95 -Paragraph 28 false 70 Accounts payable and other accrued liabilities 2 us-gaap_IncreaseDecreaseInAccountsPayableAndAccruedLiabilities us-gaap true debit duration No definition available. false false false false false false false false false false false verboselabel false 1 false true false false -3090000 -3090 false false false 2 false true false false -57350000 -57350 false false false 3 false true false false 34387000 34387 false false false xbrli:monetaryItemType monetary The net change during the reporting period in the aggregate amount of obligations and expenses incurred but not paid. Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 95 -Paragraph 28 false 71 Wages payable 2 us-gaap_IncreaseDecreaseInAccruedSalaries us-gaap true debit duration No definition available. false false false false false false false false false false false verboselabel false 1 false true false false 890000 890 false false false 2 false true false false 984000 984 false false false 3 false true false false 255000 255 false false false xbrli:monetaryItemType monetary Net change during the period in the amount of salaries accrued at the period end. Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 95 -Paragraph 28 false 72 Customer deposits and advance payments 2 wgl_CustomerDepositsAndAdvancePayments wgl false debit duration Customer deposits and advance payments false false false false false false false false false false false verboselabel false 1 false true false false 10435000 10435 false false false 2 false true false false 6834000 6834 false false false 3 false true false false -3072000 -3072 false false false xbrli:monetaryItemType monetary Customer deposits and advance payments No authoritative reference available. false 73 Accrued taxes 2 us-gaap_IncreaseDecreaseInAccruedIncomeTaxesPayable us-gaap true debit duration No definition available. false false false false false false false false false false false verboselabel false 1 false true false false -2157000 -2157 false false false 2 false true false false 4153000 4153 false false false 3 false true false false 260000 260 false false false xbrli:monetaryItemType monetary The net change during the period in the amount of cash payments due to taxing authorities for taxes that are based on the reporting entity's earnings. Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 95 -Paragraph 28 false 74 Accrued interest 2 us-gaap_IncreaseDecreaseInInterestPayableNet us-gaap true debit duration No definition available. false false false false false false false false false false false verboselabel false 1 false true false false 385000 385 false false false 2 false true false false -602000 -602 false false false 3 false true false false -16000 -16 false false false xbrli:monetaryItemType monetary The net change during the reporting period in interest payable, which represents the amount owed to note holders, bond holders, and other parties for interest earned on loans or credit extended to the reporting entity. Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 95 -Paragraph 28 false 75 Other current assets 2 us-gaap_IncreaseDecreaseInOtherOperatingAssets us-gaap true credit duration No definition available. false false false false false false false false false false true negated false 1 false true false false 3460000 3460 false false false 2 false true false false -9206000 -9206 false false false 3 false true false false 611000 611 false false false xbrli:monetaryItemType monetary The net change during the reporting period in other operating assets not otherwise defined in the taxonomy. Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 95 -Paragraph 28 false 76 Other current liabilities 2 us-gaap_IncreaseDecreaseInOtherOperatingLiabilities us-gaap true debit duration No definition available. false false false false false false false false false false false verboselabel false 1 false true false false 6785000 6785 false false false 2 false true false false -25320000 -25320 false false false 3 false true false false 19055000 19055 false false false xbrli:monetaryItemType monetary The net change during the reporting period in other operating obligations not otherwise defined in the taxonomy. Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 95 -Paragraph 28 false 77 Deferred gas costs-net 2 us-gaap_IncreaseDecreaseInDeferredGasCost us-gaap true credit duration No definition available. false false false false false false false false false false true negated false 1 false true false false 8005000 8005 false false false 2 false true false false 36801000 36801 false false false 3 false true false false -24556000 -24556 false false false xbrli:monetaryItemType monetary The net change during the reporting period in carrying amount of capitalized gas costs of a regulated entity that are expected to be recoverable through rate adjustments within one year or the normal operating cycle, if longer. Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 95 -Paragraph 28 false 78 Deferred assets-other 2 us-gaap_IncreaseDecreaseInDeferredCharges us-gaap true credit duration No definition available. false false false false false false false false false false true negated false 1 false true false false -45015000 -45015 false false false 2 false true false false -10505000 -10505 false false false 3 false true false false -13872000 -13872 false false false xbrli:monetaryItemType monetary The net change during the reporting period in the value of expenditures made during the current reporting period for benefits that will be received over a period of years. Deferred charges differ from prepaid expenses in that they usually extend over a long period of time and may or may not be regularly recurring costs of operation. Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 95 -Paragraph 28 false 79 Deferred liabilities-other 2 us-gaap_IncreaseDecreaseInOtherDeferredLiability us-gaap true debit duration No definition available. false false false false false false false false false false false verboselabel false 1 false true false false -35315000 -35315 false false false 2 false true false false -24241000 -24241 false false false 3 false true false false -4871000 -4871 false false false xbrli:monetaryItemType monetary The net change during the reporting period in other obligations not otherwise defined in the taxonomy where the payments will be made in future periods. Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 95 -Paragraph 28 false 80 Other-net 2 us-gaap_IncreaseDecreaseInOtherOperatingCapitalNet us-gaap true credit duration No definition available. false false false false false false false false false false true negatedtotal false 1 false true false false 190000 190 false false false 2 false true false false 3893000 3893 false false false 3 false true false false 850000 850 false false false xbrli:monetaryItemType monetary For entities with classified balance sheets, the net change during the reporting period in the value of other assets or liabilities used in operating activities, that are not otherwise defined in the taxonomy. For entities with unclassified balance sheets, the net change during the reporting period in the value of all other assets or liabilities used in operating activities. Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 95 -Paragraph 28 true 81 Net Cash Provided by Operating Activities 2 us-gaap_NetCashProvidedByUsedInOperatingActivities us-gaap true na duration No definition available. false false false false false false false false false false false totallabel false 1 false true false false 300911000 300911 false false false 2 false true false false 325451000 325451 false false false 3 false true false false 50221000 50221 false false false xbrli:monetaryItemType monetary The net cash from (used in) all of the entity's operating activities, including those of discontinued operations, of the reporting entity. Operating activities generally involve producing and delivering goods and providing services. Operating activity cash flows include transactions, adjustments, and changes in value that are not defined as investing or financing activities. Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 95 -Paragraph 28 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 95 -Paragraph 26 true 82 FINANCING ACTIVITIES 2 us-gaap_NetCashProvidedByUsedInFinancingActivitiesAbstract us-gaap true na duration No definition available. false false false false false true false false false false false verboselabel false 1 false false false false 0 0 false false false 2 false false false false 0 0 false false false 3 false false false false 0 0 false false false xbrli:stringItemType string No definition available. false 84 Long-term debt issued 2 us-gaap_ProceedsFromIssuanceOfLongTermDebt us-gaap true debit duration No definition available. false false false false false false false false false false false verboselabel false 1 false true false false 53018000 53018 false false false 2 false true false false 64875000 64875 false false false 3 false true false false 63285000 63285 false false false xbrli:monetaryItemType monetary The cash inflow from a debt initially having maturity due after one year or beyond the operating cycle, if longer. Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 95 -Paragraph 18 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 95 -Paragraph 19 -Subparagraph b false 85 Long-term debt retired 2 us-gaap_RepaymentsOfLongTermDebt us-gaap true credit duration No definition available. false false false false false false false false false false true negated false 1 false true false false -74019000 -74019 false false false 2 false true false false -76011000 -76011 false false false 3 false true false false -20117000 -20117 false false false xbrli:monetaryItemType monetary The cash outflow for debt initially having maturity due after one year or beyond the normal operating cycle, if longer. Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 95 -Paragraph 18 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 95 -Paragraph 20 -Subparagraph b false 86 Debt issuance costs 2 us-gaap_PaymentsOfDebtIssuanceCosts us-gaap true credit duration No definition available. false false false false false false false false false false true negated false 1 false true false false -335000 -335 false false false 2 false true false false -181000 -181 false false false 3 false false false false 0 0 false false false xbrli:monetaryItemType monetary The cash outflow paid to third parties in connection with debt origination, which will be amortized over the remaining maturity period of the associated long-term debt. Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Emerging Issues Task Force (EITF) -Number 95-13 false 87 Notes payable issued (retired)-net 2 us-gaap_ProceedsFromRepaymentsOfShortTermDebt us-gaap true debit duration No definition available. false false false false false false false false false false false verboselabel false 1 false true false false -81392000 -81392 false false false 2 false true false false -106202000 -106202 false false false 3 false true false false 108965000 108965 false false false xbrli:monetaryItemType monetary The net cash inflow (outflow) for borrowing having initial term of repayment within one year or the normal operating cycle, if longer. Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 95 -Paragraph 18 false 88 Dividends on common stock and preferred stock 2 us-gaap_PaymentsOfOrdinaryDividends us-gaap true credit duration No definition available. false false false false false false false false false false true negated false 1 false true false false -73129000 -73129 false false false 2 false true false false -71457000 -71457 false false false 3 false true false false -69711000 -69711 false false false xbrli:monetaryItemType monetary The cash outflow from distribution of an entity's earnings to common and preferred stockholders, including minority shareholders. This element excludes special dividends, which are included in a separate element for capital distributions. Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 95 -Paragraph 18 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 95 -Paragraph 20 -Subparagraph a false 89 Other financing activities-net 2 us-gaap_ProceedsFromPaymentsForOtherFinancingActivities us-gaap true debit duration No definition available. false false false false false false false false false false false totallabel false 1 false true false false -611000 -611 false false false 2 false true false false -830000 -830 false false false 3 false true false false 513000 513 false false false xbrli:monetaryItemType monetary The net cash inflow (outflow) from other financing activities. This element is used when there is not a more specific and appropriate element in the taxonomy. Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 95 -Paragraph 18, 19, 20 true 90 Net Cash Provided by (Used in) Financing Activities 2 us-gaap_NetCashProvidedByUsedInFinancingActivities us-gaap true debit duration No definition available. false false false false false false false false false false false totallabel false 1 false true false false -176468000 -176468 false false false 2 false true false false -189806000 -189806 false false false 3 false true false false 82935000 82935 false false false xbrli:monetaryItemType monetary The net cash inflow (outflow) from financing activity for the period. Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 95 -Paragraph 26 true 91 INVESTING ACTIVITIES 2 us-gaap_NetCashProvidedByUsedInInvestingActivitiesAbstract us-gaap true na duration No definition available. false false false false false true false false false false false verboselabel false 1 false false false false 0 0 false false false 2 false false false false 0 0 false false false 3 false false false false 0 0 false false false xbrli:stringItemType string No definition available. false 92 Capital expenditures (excluding Allowance for Funds Used During Construction) 2 us-gaap_PaymentsToAcquireProductiveAssets us-gaap true credit duration No definition available. false false false false false false false false false false true negatedtotal false 1 false true false false -125213000 -125213 false false false 2 false true false false -134165000 -134165 false false false 3 false true false false -133633000 -133633 false false false xbrli:monetaryItemType monetary The cash outflow for purchases of and capital improvements on property, plant and equipment (capital expenditures), software, and other intangible assets. Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 95 -Paragraph 15 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 95 -Paragraph 17 -Subparagraph c true 93 Net Cash Used in Investing Activities 2 us-gaap_NetCashProvidedByUsedInInvestingActivities us-gaap true debit duration No definition available. false false false false false false false false false false false totallabel false 1 false true false false -125213000 -125213 false false false 2 false true false false -134165000 -134165 false false false 3 false true false false -133633000 -133633 false false false xbrli:monetaryItemType monetary The net cash inflow (outflow) from investing activity. Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 95 -Paragraph 26 true 94 INCREASE IN CASH AND CASH EQUIVALENTS 2 us-gaap_CashAndCashEquivalentsPeriodIncreaseDecrease us-gaap true na duration No definition available. false false false false false false false false false false false verboselabel false 1 false true false false -770000 -770 false false false 2 false true false false 1480000 1480 false false false 3 false true false false -477000 -477 false false false xbrli:monetaryItemType monetary The net change between the beginning and ending balance of cash and cash equivalents. Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 95 -Paragraph 26 false 95 Cash and Cash Equivalents at Beginning of Year 2 us-gaap_CashAndCashEquivalentsAtCarryingValue us-gaap true debit instant No definition available. false false false false false false false false true false false periodstartlabel false 1 false true false false 5160000 5160 false false false 2 false true false false 3680000 3680 false false false 3 false true false false 4157000 4157 false false false xbrli:monetaryItemType monetary Includes currency on hand as well as demand deposits with banks or financial institutions. It also includes other kinds of accounts that have the general characteristics of demand deposits in that the Entity may deposit additional funds at any time and also effectively may withdraw funds at any time without prior notice or penalty. Cash equivalents, excluding items classified as marketable securities, include short-term, highly liquid investments that are both readily convertible to known amounts of cash, and so near their maturity that they present minimal risk of changes in value because of changes in interest rates. Generally, only investments with original maturities of three months or less qualify under that definition. Original maturity means original maturity to the entity holding the investment. For example, both a three-month US Treasury bill and a three-year Treasury note purchased three months from maturity qualify as cash equivalents. However, a Treasury note purchased three years ago does not become a cash equivalent when its remaining maturity is three months. Compensating balance arrangements that do not legally restrict the withdrawal or usage of cash amounts may be reported as Cash and Cash Equivalents, while legally restricted deposits held as compensating balances against borrowing arrangements, contracts entered into with others, or company statements of intention with regard to particular deposits should not be reported as cash and cash equivalents. Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 95 -Paragraph 7, 26 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 95 -Paragraph 8, 9 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 95 -Paragraph 7 -Footnote 1 Reference 4: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 02 -Paragraph 1 -Article 5 false 96 Cash and Cash Equivalents at End of Year 2 us-gaap_CashAndCashEquivalentsAtCarryingValue us-gaap true debit instant No definition available. false false false false false false false false false true false periodendlabel false 1 false true false false 4390000 4390 false false false 2 false true false false 5160000 5160 false false false 3 false true false false 3680000 3680 false false false xbrli:monetaryItemType monetary Includes currency on hand as well as demand deposits with banks or financial institutions. It also includes other kinds of accounts that have the general characteristics of demand deposits in that the Entity may deposit additional funds at any time and also effectively may withdraw funds at any time without prior notice or penalty. Cash equivalents, excluding items classified as marketable securities, include short-term, highly liquid investments that are both readily convertible to known amounts of cash, and so near their maturity that they present minimal risk of changes in value because of changes in interest rates. Generally, only investments with original maturities of three months or less qualify under that definition. Original maturity means original maturity to the entity holding the investment. For example, both a three-month US Treasury bill and a three-year Treasury note purchased three months from maturity qualify as cash equivalents. However, a Treasury note purchased three years ago does not become a cash equivalent when its remaining maturity is three months. Compensating balance arrangements that do not legally restrict the withdrawal or usage of cash amounts may be reported as Cash and Cash Equivalents, while legally restricted deposits held as compensating balances against borrowing arrangements, contracts entered into with others, or company statements of intention with regard to particular deposits should not be reported as cash and cash equivalents. Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 95 -Paragraph 7, 26 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 95 -Paragraph 8, 9 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 95 -Paragraph 7 -Footnote 1 Reference 4: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 02 -Paragraph 1 -Article 5 false 97 SUPPLEMENTAL DISCLOSURES OF CASH FLOW INFORMATION 2 us-gaap_SupplementalCashFlowInformationAbstract us-gaap true na duration No definition available. false false false false false true false false false false false verboselabel false 1 false false false false 0 0 false false false 2 false false false false 0 0 false false false 3 false false false false 0 0 false false false xbrli:stringItemType string No definition available. false 98 Income taxes paid - net 2 us-gaap_IncomeTaxesPaid us-gaap true credit duration No definition available. false false false false false false false false false false false verboselabel false 1 false true false false -75345000 -75345 false false false 2 false true false false 26897000 26897 false false false 3 false true false false 59108000 59108 false false false xbrli:monetaryItemType monetary The amount of cash paid during the current period to foreign, federal, state, and local authorities as taxes on income. Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 95 -Paragraph 29 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 95 -Paragraph 27 -Subparagraph f false 99 Interest paid 2 us-gaap_InterestPaid us-gaap true credit duration No definition available. false false false false false false false false false false false verboselabel false 1 false true false false 38986000 38986 false false false 2 false true false false 43615000 43615 false false false 3 false true false false 45449000 45449 false false false xbrli:monetaryItemType monetary The amount of cash paid during the current period for interest owed on money borrowed; includes amount of interest capitalized Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 95 -Paragraph 29 false 100 SUPPLEMENTAL DISCLOSURES OF NON-CASH INVESTING AND FINANCING ACTIVITIES 2 us-gaap_CashFlowNoncashInvestingAndFinancingActivitiesDisclosureAbstract us-gaap true na duration No definition available. false false false false false true false false false false false verboselabel false 1 false false false false 0 0 false false false 2 false false false false 0 0 false false false 3 false false false false 0 0 false false false xbrli:stringItemType string Designated to encapsulate the entire footnote disclosure that gives information on the supplemental cash flow activities for noncash (or part noncash) transactions for the period. Noncash is defined as information about all investing and financing activities of an enterprise during a period that affect recognized assets or liabilities but that do not result in cash receipts or cash payments in the period. "Part noncash" refers to that portion of the transaction not resulting in cash receipts or cash payments in the period. false 101 Retirement of debt related to project financing 2 us-gaap_ExtinguishmentOfDebtAmount us-gaap true debit duration No definition available. false false false false false false false false false false false verboselabel false 1 false true false false 359000 359 false false false 2 false true false false 24494000 24494 false false false 3 false false false false 0 0 false false false xbrli:monetaryItemType monetary Gross amount of debt extinguished. No authoritative reference available. false 102 Capital expenditures included in accounts payable and other accrued liabilities 2 us-gaap_CapitalExpendituresIncurredButNotYetPaid us-gaap true credit duration No definition available. false false false false false false false false false false false verboselabel false 1 true true false false 7822000 7822 false false false 2 true true false false 3473000 3473 false false false 3 true true false false 7532000 7532 false false false xbrli:monetaryItemType monetary Future cash outflow to pay for purchases of fixed assets that have occurred. No authoritative reference available. false 3 100 false Thousands UnKnown UnKnown false true