Derivative Financial Instruments - Summary of AOCI related to Cash Flow Hedges (Details) - USD ($) $ in Millions		3 Months Ended		6 Months Ended
		Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Derivative [Line Items]
Beginning Balance				$ (2,660)
Ending Balance		$ (2,633)		(2,633)
Income taxes		(72)	$ 102	143	$ 285
Cash Flow Hedging [Member]
Derivative [Line Items]
Beginning Balance		(11)	(26)		(19)
Derivative Instruments, Gain (Loss) Recognized in Other Comprehensive Income (Loss), Effective Portion, Net		(1)			(10)
Ending Balance		(12)	(26)	(12)	(26)
Cash Flow Hedging [Member] | Reclassification out of Accumulated Other Comprehensive Income [Member]
Derivative [Line Items]
Income taxes	[1]			(3)	(2)
Exelon Generation Co L L C [Member]
Derivative [Line Items]
Beginning Balance				(54)
Ending Balance		(40)		(40)
Income taxes		(158)	(31)	(31)	120
Exelon Generation Co L L C [Member] | Cash Flow Hedging [Member]
Derivative [Line Items]
Beginning Balance		(13)	(26)		(21)
Derivative Instruments, Gain (Loss) Recognized in Other Comprehensive Income (Loss), Effective Portion, Net		(1)			(7)
Ending Balance		$ (14)	(25)	$ (14)	(25)
Interest Expense [Member] | Cash Flow Hedging [Member] | Reclassification out of Accumulated Other Comprehensive Income [Member]
Derivative [Line Items]
Derivative Instruments, Loss Reclassified from Accumulated OCI into Income, Effective Portion			0		3
Interest Expense [Member] | Exelon Generation Co L L C [Member] | Cash Flow Hedging [Member] | Reclassification out of Accumulated Other Comprehensive Income [Member]
Derivative [Line Items]
Derivative Instruments, Loss Reclassified from Accumulated OCI into Income, Effective Portion			$ 1		$ 3

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