Early Plant Retirements - Pretax Expense (Details) - Facility Closing [Member] - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Three Mile Island [Member]
Accelerated depreciation	$ 71		$ 145
Accelerated nuclear fuel amortization	4		9
Operating and maintenance	0		(83)
Restructuring and Related Cost, Incurred Cost	75		71
TMI,OysterCreek [Member]
Accelerated depreciation		$ 152		$ 289
Accelerated nuclear fuel amortization		19		34
Operating and maintenance		2		28
Restructuring and Related Cost, Incurred Cost		173		351
Exelon Generation Co L L C [Member] | Three Mile Island [Member]
Accelerated depreciation	71		145
Accelerated nuclear fuel amortization	4		9
Operating and maintenance	0		(83)
Restructuring and Related Cost, Incurred Cost	$ 75		$ 71
Exelon Generation Co L L C [Member] | TMI,OysterCreek [Member]
Accelerated depreciation		152		289
Accelerated nuclear fuel amortization		19		34
Operating and maintenance		2		28
Restructuring and Related Cost, Incurred Cost		$ 173		$ 351