Early Plant Retirements - Pretax Expense (Details) - Facility Closing [Member] - USD ($) $ in Millions		3 Months Ended
		Mar. 31, 2019	Mar. 31, 2018
Three Mile Island [Member]
Accelerated depreciation	[1],[2]	$ 74
Accelerated nuclear fuel amortization	[1]	5
Operating and maintenance	[3]	(83)
Restructuring and Related Cost, Incurred Cost		(4)
TMI,OysterCreek [Member]
Accelerated depreciation	[1],[2]		$ 137
Accelerated nuclear fuel amortization	[1]		15
Operating and maintenance	[3]		26
Restructuring and Related Cost, Incurred Cost			178
Exelon Generation Co L L C [Member] | Three Mile Island [Member]
Accelerated depreciation	[1],[2]	74
Accelerated nuclear fuel amortization	[1]	5
Operating and maintenance	[3]	(83)
Restructuring and Related Cost, Incurred Cost		$ (4)
Exelon Generation Co L L C [Member] | TMI,OysterCreek [Member]
Accelerated depreciation	[1],[2]		137
Accelerated nuclear fuel amortization	[1]		15
Operating and maintenance	[3]		26
Restructuring and Related Cost, Incurred Cost			$ 178

[1] Reflects incremental accelerated depreciation and amortization for TMI for the three months ended March 31, 2019. Reflects incremental accelerated depreciation for TMI and Oyster Creek for the three months ended March 31, 2018. The Oyster Creek amounts are from February 2, 2018 through March 31, 2018.

[2] Reflects incremental accelerated depreciation of plant assets, including any ARC.

[3] In 2019, primarily reflects decrease to estimated decommissioning costs for TMI. See Note 13 — Nuclear Decommissioning for additional information on the first quarter 2019 TMI ARO update. In 2018, primarily reflects materials and supplies inventory reserve adjustments, employee related costs and CWIP impairments.