Fair Value of Financial Assets and Liabilities - Fair Value Assets And Liabilities Measured On Recurring Basis Gain Loss Included In Earnings (Details) - Fair Value, Inputs, Level 3 [Member] - USD ($) $ in Millions		3 Months Ended					6 Months Ended
		Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2016	[2]	Mar. 23, 2016	Jun. 30, 2017	Jun. 30, 2016
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	$ 423				$ 40	$ 427
Fair Value, Assets Measured on Recurring Basis, Change in Unrealized Gain (Loss)		43	(260)				106	(40)
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		(51)	(462)				37	(413)
Fair Value, Assets Measured on Recurring Basis, Change in Unrealized Gain (Loss)		0	(274)				140	(20)
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		48	34				(83)	(21)
Fair Value, Assets Measured on Recurring Basis, Change in Unrealized Gain (Loss)		43	10				(38)	(25)
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]	1	5				6	7
Fair Value, Assets Measured on Recurring Basis, Change in Unrealized Gain (Loss)	[1]	0	4				4	5
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		2	424				41	428
Fair Value, Assets Measured on Recurring Basis, Change in Unrealized Gain (Loss)		43	(261)				105	(41)
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		(51)	(462)				37	(413)
Fair Value, Assets Measured on Recurring Basis, Change in Unrealized Gain (Loss)		0	(274)				140	(20)
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		48	34				(83)	(21)
Fair Value, Assets Measured on Recurring Basis, Change in Unrealized Gain (Loss)		43	10				(38)	(25)
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]	1	4				5	6
Fair Value, Assets Measured on Recurring Basis, Change in Unrealized Gain (Loss)	[1]	0	3				3	4
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	[1]	0	1				1	1
Fair Value, Assets Measured on Recurring Basis, Change in Unrealized Gain (Loss)	[1]	0	1				1	1
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	[1]					$ (17)
Fair Value, Assets Measured on Recurring Basis, Change in Unrealized Gain (Loss)	[1]					1
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	[1]	0	1				1	2
Fair Value, Assets Measured on Recurring Basis, Change in Unrealized Gain (Loss)	[1]	0	1				1	2
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		0	(1)	$ (1)			(1)
Fair Value, Assets Measured on Recurring Basis, Change in Unrealized Gain (Loss)		0	1	$ 1			1
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)
Fair Value, Assets Measured on Recurring Basis, Change in Unrealized Gain (Loss)						1
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		0	(1)				(1)	(2)
Fair Value, Assets Measured on Recurring Basis, Change in Unrealized Gain (Loss)		$ 0	$ 1				$ 0	$ 2
Preferred Stock [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						18
Fair Value, Assets Measured on Recurring Basis, Change in Unrealized Gain (Loss)						$ 0

[1] Other, net activity consists of realized and unrealized gains (losses) included in income for the NDT funds held by Generation, accrued interest on a convertible promissory note at Generation and the life insurance contracts held by PHI and Pepco.

[2] Successor period represents activity from March 24, 2016 through June 30, 2016. See tables below for PHI's predecessor periods, as well as activity for Pepco for the three and six months ended June 30, 2017 and 2016.