Derivative Financial Instruments - Net Credit Exposure by Type of Counterparty (Details) - USD ($) $ in Millions	Dec. 31, 2016	Dec. 31, 2015
Derivative [Line Items]
Cash collateral held	$ 9
Letters of credit held	16
Exelon Generation Co L L C [Member]
Derivative [Line Items]
Cash collateral held	24	$ 21
Letters of credit held	28	$ 78
Exelon Generation Co L L C [Member] | Net Exposure [Member]
Derivative [Line Items]
Financial institutions	116
Investor-owned utilities, marketers, power producers	689
Energy cooperatives and municipalities	636
Other	71
Total	$ 1,512