Significant Accounting Policies - Summary of Capitalized Software Costs (Details) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Capitalized Software [Line Items]
Net unamortized software costs	[1]	$ 633	$ 596
Amortization of capitalized software costs	[1],[2]	208	186	$ 198
Exelon Generation Co L L C [Member]
Capitalized Software [Line Items]
Net unamortized software costs	[1]	180	193
Amortization of capitalized software costs	[1],[2]	73	59	67
Commonwealth Edison Co [Member]
Capitalized Software [Line Items]
Net unamortized software costs		172	133
Amortization of capitalized software costs		47	45	52
PECO Energy Co [Member]
Capitalized Software [Line Items]
Net unamortized software costs		86	84
Amortization of capitalized software costs		33	28	33
Baltimore Gas and Electric Company [Member]
Capitalized Software [Line Items]
Net unamortized software costs		178	163
Amortization of capitalized software costs	[2]	$ 46	$ 43	$ 36

[1] Net unamortized software costsExelon Generation ComEd PECO BGEDecember 31, 2015$633 $180 $172 $86 $178December 31, 2014596 193 133 84 163 Amortization of capitalized software costsExelon Generation ComEd PECO BGE 2015$208 $73 $47 $33 $462014186 59 45 28 432013198 67 52 33 36

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