Retirement Benefits - Defined Contribution Savings Plans (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
Pepco Holdings, LLC [Member]
Defined Benefit Plan Disclosure [Line Items]
Savings Plan Matching Contributions		$ 0	1	3		$ 2
Exelon Generation Co L L C [Member]
Defined Benefit Plan Disclosure [Line Items]
Savings Plan Matching Contributions	[1]		12		13
Commonwealth Edison Co [Member]
Defined Benefit Plan Disclosure [Line Items]
Savings Plan Matching Contributions			6		5
PECO Energy Co [Member]
Defined Benefit Plan Disclosure [Line Items]
Savings Plan Matching Contributions			2		1
Baltimore Gas and Electric Company [Member]
Defined Benefit Plan Disclosure [Line Items]
Savings Plan Matching Contributions			1		2
Business Services Company [Member]
Defined Benefit Plan Disclosure [Line Items]
Savings Plan Matching Contributions	[2]		5		$ 1
Potomac Electric Power Company [Member]
Defined Benefit Plan Disclosure [Line Items]
Savings Plan Matching Contributions			1			1
Delmarva Power and Light Company [Member]
Defined Benefit Plan Disclosure [Line Items]
Savings Plan Matching Contributions			$ 1	$ 1		0
Predecessor [Member] | Pepco Holdings, LLC [Member]
Defined Benefit Plan Disclosure [Line Items]
Savings Plan Matching Contributions						$ 3

[1] {F|ahBzfndlYmZpbGluZ3MtaHJkcmoLEgZYTUxEb2MiXlhCUkxEb2NHZW5JbmZvOmI4M2MxNDE3MDYxODRkNzQ5ZTcwNzJlZThlYmU3MWU2fFRleHRTZWxlY3Rpb246Njk4QjRCMkQ4OThEMEE4NzdFRkVGQkE2NTU2RDc3MDAM}

[2] ese 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.