Retirement Benefits - Calculation of Net Periodic Benefit Cost (Details) - USD ($) $ in Millions		3 Months Ended						6 Months Ended
		Jun. 30, 2016		Jun. 30, 2016	Mar. 23, 2016	Jun. 30, 2015		Jun. 30, 2016		Jun. 30, 2015
Defined Benefit Plan Disclosure [Line Items]
Savings Plan Matching Contributions		$ 30				$ 38		$ 56		$ 60
Pension Plan, Defined Benefit [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost		91				81		170	[1]	163
Interest cost		212				178		403	[1]	355
Expected return on assets		(292)				(256)		(555)	[1]	(513)
Amortization of:
Prior service cost (benefit)		4				4		7	[1]	7
Defined Benefit Plan, Actuarial Gain (Loss)		142				142		269	[1]	285
Net periodic benefit cost		157				149		294	[1]	297
Other Postretirement Benefit Plan, Defined Benefit [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost		28				29		54	[1]	59
Interest cost		48				42		90	[1]	83
Expected return on assets		(42)				(37)		(80)	[1]	(75)
Amortization of:
Prior service cost (benefit)		(47)				(44)		(91)	[1]	(88)
Defined Benefit Plan, Actuarial Gain (Loss)		16				21		30	[1]	41
Net periodic benefit cost		3				11		3	[1]	20
Potomac Electric Power Company [Member]
Defined Benefit Plan Disclosure [Line Items]
Savings Plan Matching Contributions		1	[2]		$ 1	1	[2]	2	[2]	2	[2]
Amortization of:
Pension and Other Postretirement Benefit Costs					7
Pepco Holdings LLC [Member]
Defined Benefit Plan Disclosure [Line Items]
Savings Plan Matching Contributions				$ 4				4
Pepco Holdings LLC [Member] | Predecessor [Member]
Defined Benefit Plan Disclosure [Line Items]
Savings Plan Matching Contributions					3	4				7
Pepco Holdings LLC [Member] | Pension Plan, Defined Benefit [Member] | Predecessor [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost					12	14				28
Interest cost					26	27				54
Expected return on assets					(30)	(35)				(70)
Amortization of:
Prior service cost (benefit)					0	1				1
Defined Benefit Plan, Actuarial Gain (Loss)					14	17				33
Net periodic benefit cost					22	24				46
Pepco Holdings LLC [Member] | Other Postretirement Benefit Plan, Defined Benefit [Member] | Predecessor [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost					1	1				3
Interest cost					6	6				12
Expected return on assets					(5)	(5)				(11)
Amortization of:
Prior service cost (benefit)					(3)	(3)				(6)
Defined Benefit Plan, Actuarial Gain (Loss)					2	1				4
Net periodic benefit cost					1	0				2
Delmarva Power and Light Company [Member]
Defined Benefit Plan Disclosure [Line Items]
Savings Plan Matching Contributions		0	[2]		1	1	[2]	1	[2]	1	[2]
Amortization of:
Pension and Other Postretirement Benefit Costs					4
Atlantic City Electric Company [Member]
Defined Benefit Plan Disclosure [Line Items]
Savings Plan Matching Contributions	[2]	1				1		1		1
Amortization of:
Pension and Other Postretirement Benefit Costs					3
Corporate, Non-Segment [Member]
Defined Benefit Plan Disclosure [Line Items]
Savings Plan Matching Contributions	[2],[3]	$ 2
Corporate, Non-Segment [Member] | Pepco Holdings LLC [Member]
Defined Benefit Plan Disclosure [Line Items]
Savings Plan Matching Contributions	[2],[3]				1	$ 1		$ 3		$ 3
Amortization of:
Pension and Other Postretirement Benefit Costs					$ 9

[1] (a)PHI net periodic benefit costs for the period prior to the merger are not included in the table above.

[2] Pepco's, DPL's and PHISCO's matching contributions for the six months ended June 30, 2016 include $1 million, $1 million,and $1 million, respectively, of costs incurred prior to the closing of Exelon’s merger with PHI on March 23, 2016, which is not included in Exelon’s matching contributions for the six months ended June 30, 2016.

[3] These amounts primarily represent amounts billed to Exelon and PHI's subsidiaries through intercompany allocations. These costs are not included in the Generation, ComEd, PECO, BGE, Pepco and DPL amounts above.