Mezzanine Equity Mezzanine Equity (Details) - USD ($)	9 Months Ended		12 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Dec. 31, 2015	Mar. 23, 2016
Redeemable Noncontrolling Interest [Line Items]
Redeemable Noncontrolling Interest, Equity, Common, Carrying Amount	$ 26,000,000		$ 28,000,000
Temporary Equity, Other Changes	107,000,000
Preferred Stock, Shares Subscribed but Unissued, Value [Abstract]
Number of preferred shares purchased			18,000
Payments to Acquire Businesses, Gross	6,896,000,000	$ 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	26,000,000		28,000,000
Temporary Equity, Other Changes	(107,000,000)
Noncontrolling Interest, Increase from Sale of Parent Equity Interest	105,000,000
Preferred Stock, Shares Subscribed but Unissued, Value [Abstract]
Payments to Acquire Businesses, Gross	$ 255,000,000	$ 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