Mezzanine Equity Mezzanine Equity (Details) - USD ($)	3 Months Ended
	Mar. 31, 2016	Mar. 23, 2016	Mar. 31, 2015	Dec. 31, 2015
Redeemable Noncontrolling Interest [Line Items]
Common Stock, Value, Issued	$ 18,686,000,000			$ 18,676,000,000
Redeemable Noncontrolling Interest, Equity, Fair Value [Abstract]
Redeemable Noncontrolling Interest, Equity, Common, Carrying Amount	$ 19,000,000			28,000,000
Preferred Stock, Shares Subscribed but Unissued, Value [Abstract]
Number of preferred shares purchased	18,000
Payments to Acquire Businesses, Gross	$ 6,645,000,000		$ 15,000,000
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, Equity, Fair Value [Abstract]
Redeemable Noncontrolling Interest, Equity, Common, Carrying Amount	19,000,000			$ 28,000,000
Temporary Equity, Other Changes	(19,000,000)
Noncontrolling Interest, Increase from Sale of Parent Equity Interest	10,000,000
Preferred Stock, Shares Subscribed but Unissued, Value [Abstract]
Payments to Acquire Businesses, Gross	$ 1,000,000		$ 15,000,000
Pepco Holdings, LLC [Member]
Preferred Stock, Shares Subscribed but Unissued, Value [Abstract]
Total mark-to-market derivative net assets (liabilities)		0
Increase (Decrease) in Derivative Assets		$ 18,000,000