Early Plant Retirements - Pretax Expense (Details) - Facility Closing [Member] - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Three Mile Island [Member]
Accelerated depreciation	$ 216		$ 250
Accelerated nuclear fuel amortization	13		12
Operating and maintenance	(53)		77
Restructuring and Related Cost, Incurred Cost	176		339
Three Mile Island [Member] | Exelon Generation Co L L C [Member]
Accelerated depreciation	216		250
Accelerated nuclear fuel amortization	13		12
Operating and maintenance	(53)		77
Restructuring and Related Cost, Incurred Cost	$ 176		$ 339
TMI, Oyster Creek [Member]
Accelerated depreciation		$ 539
Accelerated nuclear fuel amortization		57
Operating and maintenance		32
Restructuring and Related Cost, Incurred Cost		628
TMI, Oyster Creek [Member] | Exelon Generation Co L L C [Member]
Accelerated depreciation		539
Accelerated nuclear fuel amortization		57
Operating and maintenance		32
Restructuring and Related Cost, Incurred Cost		$ 628