Significant Accounting Policies - Summary of Capitalized Software Costs (Details) - USD ($)		3 Months Ended	9 Months Ended	12 Months Ended
		Mar. 23, 2016	Dec. 31, 2016	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Capitalized Software [Line Items]
Net unamortized software costs	[1]		$ 808,000,000	$ 808,000,000	$ 633,000,000
Amortization of capitalized software costs	[1]			255,000,000	208,000,000	$ 186,000,000
Pepco Holdings LLC [Member]
Capitalized Software [Line Items]
New Accounting Pronouncement or Change in Accounting Principle, Effect of Change on Net Income					34,000,000
Exelon Generation Co L L C [Member]
Capitalized Software [Line Items]
Net unamortized software costs	[1]		173,000,000	173,000,000	180,000,000
Amortization of capitalized software costs	[1]			72,000,000	73,000,000	59,000,000
Commonwealth Edison Co [Member]
Capitalized Software [Line Items]
Net unamortized software costs			213,000,000	213,000,000	172,000,000
Amortization of capitalized software costs				62,000,000	47,000,000	45,000,000
PECO Energy Co [Member]
Capitalized Software [Line Items]
Net unamortized software costs			91,000,000	91,000,000	86,000,000
Amortization of capitalized software costs				33,000,000	33,000,000	28,000,000
Baltimore Gas and Electric Company [Member]
Capitalized Software [Line Items]
Net unamortized software costs			164,000,000	164,000,000	178,000,000
Amortization of capitalized software costs				44,000,000	46,000,000	43,000,000
Potomac Electric Power Company [Member]
Capitalized Software [Line Items]
New Accounting Pronouncement or Change in Accounting Principle, Effect of Change on Net Income					4,000,000	1,000,000
Net unamortized software costs			1,000,000	1,000,000	0
Amortization of capitalized software costs				0	(2,000,000)	2,000,000
Delmarva Power and Light Company [Member]
Capitalized Software [Line Items]
New Accounting Pronouncement or Change in Accounting Principle, Effect of Change on Net Income					1,000,000
Net unamortized software costs			1,000,000	1,000,000	1,000,000
Amortization of capitalized software costs				0	0	0
Atlantic City Electric Company [Member]
Capitalized Software [Line Items]
Net unamortized software costs			1,000,000	1,000,000	1,000,000
Amortization of capitalized software costs				0	0	0
Successor [Member] | Pepco Holdings LLC [Member]
Capitalized Software [Line Items]
Net unamortized software costs			153,000,000	$ 153,000,000
Amortization of capitalized software costs			$ 29,000,000
Predecessor [Member] | Pepco Holdings LLC [Member]
Capitalized Software [Line Items]
Net unamortized software costs					172,000,000
Amortization of capitalized software costs		$ 8,000,000			$ 36,000,000	$ 30,000,000

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