Retirement Benefits - Calculation of Net Periodic Benefit Cost (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]
Savings Plan Matching Contributions		$ 26	$ 1	$ 22
Amortization of:
Pension and Other Postretirement Benefit Costs			7
Pension Plan, Defined Benefit [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost		78			$ 82
Interest cost		190			178
Expected return on assets		263			257
Amortization of:
Prior service cost (benefit)		127			143
Defined Benefit Plan, Amortization of Transition Obligations (Assets)		3			3
Net periodic benefit cost		135	22		149
Pension Plan, Defined Benefit [Member] | Predecessor [Member]
Amortization of:
Net periodic benefit cost					22
Other Postretirement Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost		26			30
Interest cost		43			42
Expected return on assets		38			38
Amortization of:
Prior service cost (benefit)		14			20
Defined Benefit Plan, Amortization of Transition Obligations (Assets)		(44)			(43)
Net periodic benefit cost		1			11
Other Postretirement Benefit Plan, Defined Benefit [Member]
Amortization of:
Net periodic benefit cost			1		2
Pepco Holdings, LLC [Member]
Defined Benefit Plan Disclosure [Line Items]
Savings Plan Matching Contributions	$ 0	1	3		2
Pepco Holdings, LLC [Member] | Predecessor [Member]
Defined Benefit Plan Disclosure [Line Items]
Savings Plan Matching Contributions					3
Pepco Holdings, LLC [Member] | Pension Plan, Defined Benefit [Member] | Predecessor [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost			12		14
Interest cost			26		27
Expected return on assets			30		35
Amortization of:
Prior service cost (benefit)			0		0
Defined Benefit Plan, Actuarial Gain (Loss)			14		16
Pepco Holdings, LLC [Member] | Other Postretirement Benefit Plan, Defined Benefit [Member] | Predecessor [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost			1		2
Interest cost			6		6
Expected return on assets			5		6
Amortization of:
Prior service cost (benefit)			(3)		(3)
Defined Benefit Plan, Actuarial Gain (Loss)			2		3
Delmarva Power and Light Company [Member]
Defined Benefit Plan Disclosure [Line Items]
Savings Plan Matching Contributions		1	1		$ 0
Amortization of:
Pension and Other Postretirement Benefit Costs			4
Atlantic City Electric Company [Member]
Amortization of:
Pension and Other Postretirement Benefit Costs			$ 3
CENG [Member]
Defined Benefit Plan Disclosure [Line Items]
Savings Plan Matching Contributions		$ 1