Supplemental Financial Information - Balance Sheet (Details) - USD ($) $ in Millions	Jun. 30, 2017		Dec. 31, 2016
Property, Plant and Equipment, Net [Abstract]
Accumulated depreciation	$ 19,735	[1]	$ 19,169	[2]
Accounts receivable, net
Allowance for uncollectible accounts	322		334
Exelon Generation Co L L C [Member]
Property, Plant and Equipment, Net [Abstract]
Accumulated depreciation	10,550	[1]	10,562	[2]
Accounts receivable, net
Allowance for uncollectible accounts	102		91
Exelon Generation Co L L C [Member] | Nuclear Fuel [Member]
Property, Plant and Equipment, Net [Abstract]
Accumulated depreciation	3,016		3,186
Commonwealth Edison Co [Member]
Property, Plant and Equipment, Net [Abstract]
Accumulated depreciation	4,122		3,937
Accounts receivable, net
Allowance for uncollectible accounts	71		70
PECO Energy Co [Member]
Property, Plant and Equipment, Net [Abstract]
Accumulated depreciation	3,330		3,253
Accounts receivable, net
Allowance for uncollectible accounts	59		61
Baltimore Gas and Electric Company [Member]
Property, Plant and Equipment, Net [Abstract]
Accumulated depreciation	3,358		3,254
Accounts receivable, net
Allowance for uncollectible accounts	26		32
Pepco Holdings LLC [Member] | Successor [Member]
Property, Plant and Equipment, Net [Abstract]
Accumulated depreciation	360		195
Accounts receivable, net
Allowance for uncollectible accounts	64		80
Potomac Electric Power Company [Member]
Property, Plant and Equipment, Net [Abstract]
Accumulated depreciation	3,131		3,050
Accounts receivable, net
Allowance for uncollectible accounts	25		29
Delmarva Power and Light Company [Member]
Property, Plant and Equipment, Net [Abstract]
Accumulated depreciation	1,212		1,175
Accounts receivable, net
Allowance for uncollectible accounts	19		24
Atlantic City Electric Company [Member]
Property, Plant and Equipment, Net [Abstract]
Accumulated depreciation	1,042		1,016
Accounts receivable, net
Allowance for uncollectible accounts	$ 20		$ 27

[1] Includes accumulated amortization of nuclear fuel in the reactor core of $3,016 million

[2] Includes accumulated amortization of nuclear fuel in the reactor core of $3,186 million