Early Plant Retirements - Pretax Expense (Details) - Facility Closing [Member] - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Three Mile Island [Member]
Accelerated depreciation	$ 71		$ 216
Accelerated nuclear fuel amortization	3		13
Operating and maintenance	39		(44)
Restructuring and Related Cost, Incurred Cost	113		185
TMI,OysterCreek [Member]
Accelerated depreciation		$ 152		$ 441
Accelerated nuclear fuel amortization		18		52
Operating and maintenance		4		32
Restructuring and Related Cost, Incurred Cost		174		525
Exelon Generation Co L L C [Member] | Three Mile Island [Member]
Accelerated depreciation	71		216
Accelerated nuclear fuel amortization	3		13
Operating and maintenance	39		(44)
Restructuring and Related Cost, Incurred Cost	$ 113		$ 185
Exelon Generation Co L L C [Member] | TMI,OysterCreek [Member]
Accelerated depreciation		152		441
Accelerated nuclear fuel amortization		18		52
Operating and maintenance		4		32
Restructuring and Related Cost, Incurred Cost		$ 174		$ 525