Retirement Benefits - Allocated Portion of Pension and Postretirement Benefit Plan Costs (Details) - USD ($) $ in Millions		3 Months Ended
	Mar. 31, 2016	Mar. 31, 2016		Mar. 23, 2016	Dec. 31, 2015		Mar. 31, 2015
Defined Benefit Plan Disclosure [Line Items]
Pension and Other Postretirement Benefit Expense		$ 136					$ 159
Other Segment [Member]
Defined Benefit Plan Disclosure [Line Items]
Pension and Other Postretirement Benefit Expense		14			$ 14
Pepco Holdings, LLC [Member]
Defined Benefit Plan Disclosure [Line Items]
Pension and Other Postretirement Benefit Expense	$ 3			$ 23
Pepco Holdings, LLC [Member] | Other Segment [Member]
Defined Benefit Plan Disclosure [Line Items]
Pension and Other Postretirement Benefit Expense		9					8
Exelon Generation Co L L C [Member]
Defined Benefit Plan Disclosure [Line Items]
Pension and Other Postretirement Benefit Expense		54	[1]		67	[1]	67
Commonwealth Edison Co [Member]
Defined Benefit Plan Disclosure [Line Items]
Pension and Other Postretirement Benefit Expense		41			52		52
PECO Energy Co [Member]
Defined Benefit Plan Disclosure [Line Items]
Pension and Other Postretirement Benefit Expense		8			10		10
Baltimore Gas and Electric Company [Member]
Defined Benefit Plan Disclosure [Line Items]
Pension and Other Postretirement Benefit Expense		16			$ 17		16
Potomac Electric Power Company [Member]
Defined Benefit Plan Disclosure [Line Items]
Pension and Other Postretirement Benefit Expense		8					8
Delmarva Power and Light Company [Member]
Defined Benefit Plan Disclosure [Line Items]
Pension and Other Postretirement Benefit Expense		5					4
Atlantic City Electric Company [Member]
Defined Benefit Plan Disclosure [Line Items]
Pension and Other Postretirement Benefit Expense		$ 4					4
Predecessor [Member] | Pepco Holdings, LLC [Member]
Defined Benefit Plan Disclosure [Line Items]
Pension and Other Postretirement Benefit Expense							$ 24

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