Label	Element	Value
Pepco Holdings LLC [Member] | Successor [Member]
Net Cash Provided by (Used in) Operating Activities	us-gaap_NetCashProvidedByUsedInOperatingActivities	$ 888,000,000
Increase (Decrease) in Receivables	us-gaap_IncreaseDecreaseInReceivables	21,000,000
Increase (Decrease) in Inventories	us-gaap_IncreaseDecreaseInInventories	(3,000,000)
Proceeds from (Repayments of) Short-term Debt	us-gaap_ProceedsFromRepaymentsOfShortTermDebt	(515,000,000)
Increase (Decrease) in Income Taxes Payable	us-gaap_IncreaseDecreaseInAccruedIncomeTaxesPayable	(22,000,000)
Increase (Decrease) in Accounts Payable and Accrued Liabilities	us-gaap_IncreaseDecreaseInAccountsPayableAndAccruedLiabilities	19,000,000
Net Cash Provided by (Used in) Investing Activities	us-gaap_NetCashProvidedByUsedInInvestingActivities	(1,030,000,000)
Payments to Acquire Property, Plant, and Equipment	us-gaap_PaymentsToAcquirePropertyPlantAndEquipment	1,008,000,000
Proceeds from (Repayments of) Short-term Debt, Maturing in Three Months or Less	us-gaap_ProceedsFromRepaymentsOfShortTermDebtMaturingInThreeMonthsOrLess	0
Increase (Decrease) in Due to Affiliates	us-gaap_IncreaseDecreaseInDueToAffiliates	(6,000,000)
Other Noncash Income (Expense)	us-gaap_OtherNoncashIncomeExpense	(514,000,000)
Repayments of Long-term Debt	us-gaap_RepaymentsOfLongTermDebt	338,000,000
Payments to Acquire Marketable Securities	us-gaap_PaymentsToAcquireMarketableSecurities	0
Repayments of Debt, Maturing in More than Three Months	us-gaap_RepaymentsOfDebtMaturingInMoreThanThreeMonths	300,000,000
Proceeds from Sale of Property Held-for-sale	us-gaap_ProceedsFromSaleOfPropertyHeldForSale	24,000,000
Unrealized Gain (Loss) on Derivatives	us-gaap_UnrealizedGainLossOnDerivatives	0
Change Receivables Payables From Affiliates	exc_ChangeReceivablesPayablesFromAffiliates	42,000,000
Proceeds from (Payments for) Other Financing Activities	us-gaap_ProceedsFromPaymentsForOtherFinancingActivities	(5,000,000)
Income (Loss) from Discontinued Operations, Net of Tax, Including Portion Attributable to Noncontrolling Interest	us-gaap_IncomeLossFromDiscontinuedOperationsNetOfTax	0
Net Cash Provided by (Used in) Financing Activities	us-gaap_NetCashProvidedByUsedInFinancingActivities	(7,000,000)
Deferred Income Taxes and Tax Credits	us-gaap_DeferredIncomeTaxesAndTaxCredits	295,000,000
Payments for (Proceeds from) Other Investing Activities	us-gaap_PaymentsForProceedsFromOtherInvestingActivities	9,000,000
Increase (Decrease) in Other Operating Assets and Liabilities, Net	us-gaap_IncreaseDecreaseInOtherOperatingCapitalNet	311,000,000
Proceeds from Stock Plans	us-gaap_ProceedsFromStockPlans	0
Increase (Decrease) in Restricted Cash	us-gaap_IncreaseDecreaseInRestrictedCash	37,000,000
Proceeds from Issuance of Long-term Debt	us-gaap_ProceedsFromIssuanceOfLongTermDebt	179,000,000
Cash and Cash Equivalents, Period Increase (Decrease)	us-gaap_CashAndCashEquivalentsPeriodIncreaseDecrease	(149,000,000)
Proceeds from Issuance of Preferred Stock and Preference Stock	us-gaap_ProceedsFromIssuanceOfPreferredStockAndPreferenceStock	0
Pepco Holdings LLC [Member] | Predecessor [Member]
Net Cash Provided by (Used in) Operating Activities	us-gaap_NetCashProvidedByUsedInOperatingActivities	264,000,000
Increase (Decrease) in Receivables	us-gaap_IncreaseDecreaseInReceivables	28,000,000
Proceeds from Contributions from Parent	us-gaap_ProceedsFromContributionsFromParent	0
Increase (Decrease) in Inventories	us-gaap_IncreaseDecreaseInInventories	4,000,000
Payments of Ordinary Dividends, Common Stock	us-gaap_PaymentsOfDividendsCommonStock	0
Proceeds from (Repayments of) Short-term Debt	us-gaap_ProceedsFromRepaymentsOfShortTermDebt	(121,000,000)
Increase (Decrease) in Income Taxes Payable	us-gaap_IncreaseDecreaseInAccruedIncomeTaxesPayable	12,000,000
Increase (Decrease) in Accounts Payable and Accrued Liabilities	us-gaap_IncreaseDecreaseInAccountsPayableAndAccruedLiabilities	42,000,000
Cash and Cash Equivalents, at Carrying Value	us-gaap_CashAndCashEquivalentsAtCarryingValue	319,000,000
Cash and Cash Equivalents, at Carrying Value	us-gaap_CashAndCashEquivalentsAtCarryingValue	319,000,000
Net Cash Provided by (Used in) Investing Activities	us-gaap_NetCashProvidedByUsedInInvestingActivities	(343,000,000)
Impairment of Long-Lived Assets Held-for-use	us-gaap_ImpairmentOfLongLivedAssetsHeldForUse	0
Payments to Acquire Property, Plant, and Equipment	us-gaap_PaymentsToAcquirePropertyPlantAndEquipment	273,000,000
Proceeds from (Repayments of) Short-term Debt, Maturing in Three Months or Less	us-gaap_ProceedsFromRepaymentsOfShortTermDebtMaturingInThreeMonthsOrLess	500,000,000
Increase (Decrease) in Due to Affiliates	us-gaap_IncreaseDecreaseInDueToAffiliates	0
Other Noncash Income (Expense)	us-gaap_OtherNoncashIncomeExpense	(46,000,000)
Repayments of Long-term Debt	us-gaap_RepaymentsOfLongTermDebt	11,000,000
Payments to Acquire Marketable Securities	us-gaap_PaymentsToAcquireMarketableSecurities	68,000,000
Repayments of Debt, Maturing in More than Three Months	us-gaap_RepaymentsOfDebtMaturingInMoreThanThreeMonths	0
Proceeds from Sale of Property Held-for-sale	us-gaap_ProceedsFromSaleOfPropertyHeldForSale	0
Unrealized Gain (Loss) on Derivatives	us-gaap_UnrealizedGainLossOnDerivatives	(18,000,000)
Change Receivables Payables From Affiliates	exc_ChangeReceivablesPayablesFromAffiliates	0
Proceeds from (Payments for) Other Financing Activities	us-gaap_ProceedsFromPaymentsForOtherFinancingActivities	2,000,000
Income (Loss) from Discontinued Operations, Net of Tax, Including Portion Attributable to Noncontrolling Interest	us-gaap_IncomeLossFromDiscontinuedOperationsNetOfTax	0
Net Cash Provided by (Used in) Financing Activities	us-gaap_NetCashProvidedByUsedInFinancingActivities	372,000,000
Deferred Income Taxes and Tax Credits	us-gaap_DeferredIncomeTaxesAndTaxCredits	19,000,000
Payments for (Proceeds from) Other Investing Activities	us-gaap_PaymentsForProceedsFromOtherInvestingActivities	5,000,000
Increase (Decrease) in Other Operating Assets and Liabilities, Net	us-gaap_IncreaseDecreaseInOtherOperatingCapitalNet	8,000,000
Proceeds from Stock Plans	us-gaap_ProceedsFromStockPlans	2,000,000
Increase (Decrease) in Restricted Cash	us-gaap_IncreaseDecreaseInRestrictedCash	(3,000,000)
Proceeds from Issuance of Long-term Debt	us-gaap_ProceedsFromIssuanceOfLongTermDebt	0
Cash and Cash Equivalents, Period Increase (Decrease)	us-gaap_CashAndCashEquivalentsPeriodIncreaseDecrease	293,000,000
Proceeds from Issuance of Preferred Stock and Preference Stock	us-gaap_ProceedsFromIssuanceOfPreferredStockAndPreferenceStock	0
Payments of Distributions to Affiliates	us-gaap_PaymentsOfDistributionsToAffiliates	0
AOCI Attributable to Parent [Member] | Pepco Holdings LLC [Member] | Successor [Member]
Limited Liability Company (LLC) Members' Equity, Including Portion Attributable to Noncontrolling Interest	us-gaap_LimitedLiabilityCompanyLlcMembersEquityIncludingPortionAttributableToNoncontrollingInterest	0
Undistributed Earnings [Member] | Pepco Holdings LLC [Member] | Successor [Member]
Limited Liability Company (LLC) Members' Equity, Including Portion Attributable to Noncontrolling Interest	us-gaap_LimitedLiabilityCompanyLlcMembersEquityIncludingPortionAttributableToNoncontrollingInterest	0
Membership Interest [Member] | Pepco Holdings LLC [Member] | Successor [Member]
Limited Liability Company (LLC) Members' Equity, Including Portion Attributable to Noncontrolling Interest	us-gaap_LimitedLiabilityCompanyLlcMembersEquityIncludingPortionAttributableToNoncontrollingInterest	$ 7,200,000,000