Fair Value of Financial Assets and Liabilities - Fair Value Assets And Liabilities Measured On Recurring Basis Gain Loss Included In Earnings (Details) - USD ($)		3 Months Ended			6 Months Ended	9 Months Ended
		Sep. 30, 2016	Mar. 23, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2016	Sep. 30, 2015
Operating Revenue [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis Gain Loss Included In Earnings [Line Items]
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Gain (Loss) Included in Earnings		$ 180,000,000		$ (4,000,000)		$ (232,000,000)	$ (31,000,000)
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Gain (Loss) Included in Other Comprehensive Income (Loss)		323,000,000		198,000,000		303,000,000	538,000,000
Purchased Power And Fuel [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis Gain Loss Included In Earnings [Line Items]
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Gain (Loss) Included in Earnings		(85,000,000)		(44,000,000)		(107,000,000)	(56,000,000)
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Gain (Loss) Included in Other Comprehensive Income (Loss)		(38,000,000)		(17,000,000)		(63,000,000)	(2,000,000)
Other, net [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis Gain Loss Included In Earnings [Line Items]
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Gain (Loss) Included in Earnings	[1]	(3,000,000)		0		4,000,000	4,000,000
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Gain (Loss) Included in Other Comprehensive Income (Loss)	[1]	3,000,000		(1,000,000)		8,000,000	2,000,000
Exelon Generation Co L L C [Member] | Operating Revenue [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis Gain Loss Included In Earnings [Line Items]
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Gain (Loss) Included in Earnings		180,000,000		(4,000,000)		(232,000,000)	(31,000,000)
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Gain (Loss) Included in Other Comprehensive Income (Loss)		323,000,000		198,000,000		303,000,000	538,000,000
Exelon Generation Co L L C [Member] | Purchased Power And Fuel [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis Gain Loss Included In Earnings [Line Items]
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Gain (Loss) Included in Earnings		(85,000,000)		(44,000,000)		(107,000,000)	(56,000,000)
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Gain (Loss) Included in Other Comprehensive Income (Loss)		(38,000,000)		(17,000,000)		(63,000,000)	(2,000,000)
Exelon Generation Co L L C [Member] | Other, net [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis Gain Loss Included In Earnings [Line Items]
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Gain (Loss) Included in Earnings	[1]	(4,000,000)		0		2,000,000	4,000,000
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Gain (Loss) Included in Other Comprehensive Income (Loss)	[1]	3,000,000		(1,000,000)		7,000,000	2,000,000
Pepco Holdings LLC [Member] | Other, net [Member] | Successor [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis Gain Loss Included In Earnings [Line Items]
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Gain (Loss) Included in Earnings					$ 2,000,000
Fair Value, Assets Measured on Recurring Basis, Change in Unrealized Gain (Loss)					1,000,000
Pepco Holdings LLC [Member] | Other, net [Member] | Predecessor [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis Gain Loss Included In Earnings [Line Items]
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Gain (Loss) Included in Earnings							19,000,000
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Gain (Loss) Included in Other Comprehensive Income (Loss)							17,000,000
Potomac Electric Power Company [Member] | Other, net [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis Gain Loss Included In Earnings [Line Items]
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Gain (Loss) Included in Earnings							4,000,000
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Gain (Loss) Included in Other Comprehensive Income (Loss)							2,000,000
6311 Life Insurance [Member] | Delmarva Power and Light Company [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis Gain Loss Included In Earnings [Line Items]
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Gain (Loss) Included in Earnings							0
Fair Value, Assets Measured on Recurring Basis, Change in Unrealized Gain (Loss)							0
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Purchases							0
6311 Life Insurance [Member] | Pepco Holdings LLC [Member] | Successor [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis Gain Loss Included In Earnings [Line Items]
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Purchases					(1,000,000)
6311 Life Insurance [Member] | Pepco Holdings LLC [Member] | Predecessor [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis Gain Loss Included In Earnings [Line Items]
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Gain (Loss) Included in Earnings			$ 0
6311 Life Insurance [Member] | Potomac Electric Power Company [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis Gain Loss Included In Earnings [Line Items]
Fair Value, Assets Measured on Recurring Basis, Change in Unrealized Gain (Loss)						2,000,000	2,000,000
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Purchases		0		(3,000,000)		(1,000,000)	(4,000,000)
Fair Value, Inputs, Level 3 [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis Gain Loss Included In Earnings [Line Items]
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Gain (Loss) Included in Earnings		93,000,000		(48,000,000)		(334,000,000)	(83,000,000)
Fair Value, Assets Measured on Recurring Basis, Change in Unrealized Gain (Loss)		288,000,000		180,000,000		248,000,000	538,000,000
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Purchases		214,000,000		67,000,000		420,000,000	259,000,000
Fair Value, Inputs, Level 3 [Member] | Exelon Generation Co L L C [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis Gain Loss Included In Earnings [Line Items]
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Gain (Loss) Included in Earnings		92,000,000		(48,000,000)		(336,000,000)	(83,000,000)
Fair Value, Assets Measured on Recurring Basis, Change in Unrealized Gain (Loss)		288,000,000		180,000,000		247,000,000	538,000,000
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Purchases		214,000,000		67,000,000		420,000,000	259,000,000
Fair Value, Inputs, Level 3 [Member] | Pepco Holdings LLC [Member] | Successor [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis Gain Loss Included In Earnings [Line Items]
Fair Value, Assets Measured on Recurring Basis, Change in Unrealized Gain (Loss)		0
Fair Value, Inputs, Level 3 [Member] | Pepco Holdings LLC [Member] | Predecessor [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis Gain Loss Included In Earnings [Line Items]
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Gain (Loss) Included in Earnings				16,000,000
Fair Value, Assets Measured on Recurring Basis, Change in Unrealized Gain (Loss)				15,000,000
Fair Value, Inputs, Level 3 [Member] | Potomac Electric Power Company [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis Gain Loss Included In Earnings [Line Items]
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Gain (Loss) Included in Earnings		1,000,000		1,000,000
Fair Value, Assets Measured on Recurring Basis, Change in Unrealized Gain (Loss)		0		0
Fair Value, Inputs, Level 3 [Member] | 6311 Life Insurance [Member] | Pepco Holdings LLC [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis Gain Loss Included In Earnings [Line Items]
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Gain (Loss) Included in Earnings					(2,000,000)
Fair Value, Inputs, Level 3 [Member] | 6311 Life Insurance [Member] | Pepco Holdings LLC [Member] | Successor [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis Gain Loss Included In Earnings [Line Items]
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Gain (Loss) Included in Earnings		1,000,000
Fair Value, Assets Measured on Recurring Basis, Change in Unrealized Gain (Loss)		0			1,000,000
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Purchases		$ 0			$ 0
Fair Value, Inputs, Level 3 [Member] | 6311 Life Insurance [Member] | Pepco Holdings LLC [Member] | Predecessor [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis Gain Loss Included In Earnings [Line Items]
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Gain (Loss) Included in Earnings			1,000,000	1,000,000			4,000,000
Fair Value, Assets Measured on Recurring Basis, Change in Unrealized Gain (Loss)			1,000,000	0			2,000,000
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Purchases			$ 0	(2,000,000)			(3,000,000)
Fair Value, Inputs, Level 3 [Member] | 6311 Life Insurance [Member] | Potomac Electric Power Company [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis Gain Loss Included In Earnings [Line Items]
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Gain (Loss) Included in Earnings				1,000,000
Fair Value, Assets Measured on Recurring Basis, Change in Unrealized Gain (Loss)				$ 0
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Purchases						$ 3,000,000	$ 4,000,000

[1] Other, net activity consists of realized and unrealized gains (losses) included in income for the NDT funds held by Generation and the life insurance contracts held by Pepco.