Mezzanine Equity Mezzanine Equity (Details) - USD ($)	3 Months Ended	6 Months Ended
	Mar. 23, 2016	Jun. 30, 2016	Jun. 30, 2015	Dec. 31, 2015
Redeemable Noncontrolling Interest [Line Items]
Redeemable Noncontrolling Interest, Equity, Common, Carrying Amount		$ 24,000,000		$ 28,000,000
Temporary Equity, Other Changes		$ 56,000,000
Preferred Stock, Shares Subscribed but Unissued, Value [Abstract]
Number of preferred shares purchased		18,000
Payments to Acquire Businesses, Gross		$ 6,642,000,000	$ 28,000,000
Preferred Stock [Member]
Preferred Stock, Shares Subscribed but Unissued, Value [Abstract]
Payments to Acquire Businesses, Gross	$ 180,000,000
Exelon Generation Co L L C [Member]
Redeemable Noncontrolling Interest [Line Items]
Redeemable Noncontrolling Interest, Equity, Common, Carrying Amount		24,000,000		$ 28,000,000
Temporary Equity, Other Changes		(56,000,000)
Noncontrolling Interest, Increase from Sale of Parent Equity Interest		52,000,000
Preferred Stock, Shares Subscribed but Unissued, Value [Abstract]
Payments to Acquire Businesses, Gross		$ 1,000,000	$ 28,000,000
Pepco Holdings LLC [Member]
Preferred Stock, Shares Subscribed but Unissued, Value [Abstract]
Derivative, Fair Value, Net	0
Increase (Decrease) in Derivative Assets	$ 18,000,000