Derivative Financial Instruments Schedule of Notional Amounts Outstanding (Details) - USD ($) $ in Millions	Jun. 30, 2018	Dec. 31, 2017
Cash Flow Hedging [Member] | Designated as Hedging Instrument [Member] | Interest Rate Swap [Member]
Derivative [Line Items]
Derivative, Notional Amount	$ 624	$ 636
Fair Value Hedging [Member] | Interest Rate Swap [Member]
Derivative [Line Items]
Derivative, Notional Amount	800	800
Exelon Generation Co L L C [Member] | Foreign Exchange Contract [Member]
Derivative [Line Items]
Derivative, Notional Amount	$ 86	$ 94