Derivative Financial Instruments Schedule of Notional Amounts Outstanding (Details) - USD ($) $ in Millions		Sep. 30, 2018	Dec. 31, 2017
Fair Value Hedging [Member] | Corporate, Non-Segment [Member] | Interest Rate Swap [Member]
Derivative [Line Items]
Derivative, Notional Amount		$ 0	$ 800	[1]
Cash Flow Hedging [Member] | Exelon Generation Co L L C [Member] | Interest Rate Swap [Member]
Derivative [Line Items]
Derivative, Notional Amount	[1]	0	636
Not Designated as Hedging Instrument, Economic Hedge [Member]
Derivative [Line Items]
Derivative, Notional Amount		1,513	95
Not Designated as Hedging Instrument, Economic Hedge [Member] | Foreign Exchange Contract [Member]
Derivative [Line Items]
Derivative, Notional Amount		88	94
Not Designated as Hedging Instrument, Economic Hedge [Member] | Interest Rate Swap [Member]
Derivative [Line Items]
Derivative, Notional Amount		1,425	1	[1]
Not Designated as Hedging Instrument, Economic Hedge [Member] | Exelon Generation Co L L C [Member]
Derivative [Line Items]
Derivative, Notional Amount		713	95
Not Designated as Hedging Instrument, Economic Hedge [Member] | Exelon Generation Co L L C [Member] | Foreign Exchange Contract [Member]
Derivative [Line Items]
Derivative, Notional Amount		88	94
Not Designated as Hedging Instrument, Economic Hedge [Member] | Exelon Generation Co L L C [Member] | Interest Rate Swap [Member]
Derivative [Line Items]
Derivative, Notional Amount		625	1
Not Designated as Hedging Instrument, Economic Hedge [Member] | Corporate, Non-Segment [Member]
Derivative [Line Items]
Derivative, Notional Amount		800	0
Not Designated as Hedging Instrument, Economic Hedge [Member] | Corporate, Non-Segment [Member] | Foreign Exchange Contract [Member]
Derivative [Line Items]
Derivative, Notional Amount		0	0
Not Designated as Hedging Instrument, Economic Hedge [Member] | Corporate, Non-Segment [Member] | Interest Rate Swap [Member]
Derivative [Line Items]
Derivative, Notional Amount		$ 800	$ 0

[1] On July 1, 2018, Exelon and Generation de-designated its fair value and cash flow hedges. The table excludes amounts of $800 million of fixed-to-floating hedges that were previously designated as fair value hedges by Exelon and $636 million of floating-to-fixed hedges that were previously designated as cash flow hedges by Exelon and Generation as of December 31, 2017.