Mezzanine Equity Contingently Redeemable Noncontrolling Interest (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Noncontrolling Interest [Line Items]
Business Acquisition, Equity Interest Issued or Issuable, Number of Shares	18,000
Noncontrolling Interest, Increase from Sale of Parent Equity Interest	$ 396		$ 1,548
Redeemable Noncontrolling Interest, Equity, Common, Carrying Amount	0	$ 28
Temporary Equity, Other Changes		4	(528)
Payments to Acquire Businesses, Gross	6,934	40	386
Pepco Holdings LLC [Member]
Noncontrolling Interest [Line Items]
Derivative Asset, Not Subject to Master Netting Arrangement	18
Exelon Generation Co L L C [Member]
Noncontrolling Interest [Line Items]
Noncontrolling Interest, Increase from Sale of Parent Equity Interest	396	1	5
Redeemable Noncontrolling Interest, Equity, Common, Carrying Amount	0	28	0
Temporary Equity, Accretion to Redemption Value	129	32
Temporary Equity, Other Changes	(157)		(4)
Payments to Acquire Businesses, Gross	$ 293	$ 40	$ 386