Revenue from Contracts with Customers - Change in Contract with Customer, Asset and Liability (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019	Dec. 31, 2019	Dec. 31, 2018
Change in Contract with Customer, Asset and Liability [Line Items]
Contract Assets	$ 172	$ 187	$ 174	$ 187
Contract Liabilities	29	25	33	27
Consideration (received) due, contract assets	(19)	(26)
Consideration received (due), contract liabilities	20	21
Revenues recognized, contract assets	17	26
Contract with Customer, Liability, Revenue Recognized	(24)	(23)
Contract with Customer, Performance Obligation Satisfied in Previous Period	9	5
Exelon Generation Co L L C [Member]
Change in Contract with Customer, Asset and Liability [Line Items]
Contract Assets	172	187	174	187
Contract Liabilities	56	39	$ 71	$ 42
Consideration (received) due, contract assets	(19)	(26)
Consideration received (due), contract liabilities	55	63
Revenues recognized, contract assets	17	26
Contract with Customer, Liability, Revenue Recognized	(70)	(66)
Contract with Customer, Performance Obligation Satisfied in Previous Period	$ 19	$ 5