Derivative Financial Instruments - Summary of AOCI related to Cash Flow Hedges (Details) - USD ($) $ in Millions		3 Months Ended			9 Months Ended
		Sep. 30, 2017		Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Derivative [Line Items]
Beginning Balance					$ (2,660)
Ending Balance		$ (2,589)			(2,589)
Income taxes		452		$ 340	595	$ 625
Cash Flow Hedging [Member]
Derivative [Line Items]
Beginning Balance		(12)		(26)		(19)
Derivative Instruments, Gain (Loss) Recognized in Other Comprehensive Income (Loss), Effective Portion, Net		1		3		(1)
Ending Balance		(12)		(23)	(12)	(23)
Exelon Generation Co L L C [Member]
Derivative [Line Items]
Beginning Balance					(54)
Ending Balance		(36)			(36)
Income taxes		240		173	209	293
Exelon Generation Co L L C [Member] | Cash Flow Hedging [Member]
Derivative [Line Items]
Beginning Balance		(14)		(25)		(21)
Derivative Instruments, Gain (Loss) Recognized in Other Comprehensive Income (Loss), Effective Portion, Net		1		1		0
Ending Balance		(14)		(24)	(14)	(24)
Interest Expense [Member] | Cash Flow Hedging [Member]
Derivative [Line Items]
Derivative Instruments, Gain (Loss) Reclassified from Accumulated OCI into Income, Effective Portion, Net		(1)	[1]			(3)	[2]
Interest Expense [Member] | Exelon Generation Co L L C [Member] | Cash Flow Hedging [Member]
Derivative [Line Items]
Derivative Instruments, Gain (Loss) Reclassified from Accumulated OCI into Income, Effective Portion, Net		(1)	[1]			(3)	[2]
Reclassification out of Accumulated Other Comprehensive Income [Member]
Derivative [Line Items]
Income taxes	[3]			0		0
Reclassification out of Accumulated Other Comprehensive Income [Member] | Cash Flow Hedging [Member]
Derivative [Line Items]
Income taxes		1			(2)	(2)
Reclassification out of Accumulated Other Comprehensive Income [Member] | Cash Flow Hedging [Member] | Accumulated Net Gain (Loss) from Cash Flow Hedges Attributable to Parent [Member]
Derivative [Line Items]
Income taxes	[3]	(1)		1	2	3
Reclassification out of Accumulated Other Comprehensive Income [Member] | Exelon Generation Co L L C [Member]
Derivative [Line Items]
Income taxes	[3]			0		0
Reclassification out of Accumulated Other Comprehensive Income [Member] | Exelon Generation Co L L C [Member] | Cash Flow Hedging [Member] | Accumulated Net Gain (Loss) from Cash Flow Hedges Attributable to Parent [Member]
Derivative [Line Items]
Income taxes	[3]	$ (1)		$ 1	$ 2	$ 3

[1] Amount is net of related income tax benefit of $1 million for the three months ended September 30, 2017.

[2] Amount is net of related income tax expense of $2 million for the nine months ended September 30, 2016.

[3] Amounts in parenthesis represent a decrease in net income.