Fair Value of Financial Assets and Liabilities - Fair Value Assets And Liabilities Measured On Recurring Basis Gain Loss Included In Earnings (Details) - USD ($) $ in Millions		3 Months Ended				6 Months Ended
		Jun. 30, 2018		Jun. 30, 2017		Jun. 30, 2018		Jun. 30, 2017
Pepco Holdings LLC [Member] | Operating and Maintenance [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				$ 2
Fair Value, Assets Measured on Recurring Basis, Change in Unrealized Gain (Loss)		0				0
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		112		$ 2		(75)		$ 40
Fair Value, Assets Measured on Recurring Basis, Change in Unrealized Gain (Loss)		3		43		260		106
Fair Value, Inputs, Level 3 [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		(191)		(51)		144		37
Fair Value, Assets Measured on Recurring Basis, Change in Unrealized Gain (Loss)		(71)		0		238		140
Fair Value, Inputs, Level 3 [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		78		48		(73)		(83)
Fair Value, Assets Measured on Recurring Basis, Change in Unrealized Gain (Loss)		78		43		25		(38)
Fair Value, Inputs, Level 3 [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		2		6
Fair Value, Assets Measured on Recurring Basis, Change in Unrealized Gain (Loss)	[1]	(4)		0		(3)		4
Fair Value, Inputs, Level 3 [Member] | Operating and Maintenance [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				2
Fair Value, Assets Measured on Recurring Basis, Change in Unrealized Gain (Loss)		0				0
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		113		2		(73)		41
Fair Value, Assets Measured on Recurring Basis, Change in Unrealized Gain (Loss)		3		43		260		105
Fair Value, Inputs, Level 3 [Member] | 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		(191)		(51)		144		37
Fair Value, Assets Measured on Recurring Basis, Change in Unrealized Gain (Loss)		(71)		0		238		140
Fair Value, Inputs, Level 3 [Member] | 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		78		48		(73)		(83)
Fair Value, Assets Measured on Recurring Basis, Change in Unrealized Gain (Loss)		78		43		25		(38)
Fair Value, Inputs, Level 3 [Member] | 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]	0		1		2		5
Fair Value, Assets Measured on Recurring Basis, Change in Unrealized Gain (Loss)	[1]	(4)		0		(3)		3
Fair Value, Inputs, Level 3 [Member] | Pepco Holdings LLC [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
Fair Value, Assets Measured on Recurring Basis, Change in Unrealized Gain (Loss)	[1]			0				1
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		1	[2]	0	[3]	2	[2]	1	[3]
Fair Value, Assets Measured on Recurring Basis, Change in Unrealized Gain (Loss)		$ 0	[2]	$ 0	[3]	$ 0	[2]	$ 1	[3]

[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] The amounts represented are life insurance contracts at Pepco.

[3] The amounts represented are life insurance contracts at Pepco.