Supplemental Financial Information - Balance Sheet (Details) - USD ($) $ in Millions	Mar. 31, 2017		Dec. 31, 2016
Property, Plant and Equipment, Net [Abstract]
Accumulated depreciation	$ 19,716	[1]	$ 19,169	[2]
Accounts receivable, net
Allowance for uncollectible accounts	346		334
Exelon Generation Co L L C [Member]
Property, Plant and Equipment, Net [Abstract]
Accumulated depreciation	10,801	[1]	10,562	[2]
Accounts receivable, net
Allowance for uncollectible accounts	97		91
Exelon Generation Co L L C [Member] | Nuclear Fuel [Member]
Property, Plant and Equipment, Net [Abstract]
Accumulated depreciation	3,171		3,186
Commonwealth Edison Co [Member]
Property, Plant and Equipment, Net [Abstract]
Accumulated depreciation	4,040		3,937
Accounts receivable, net
Allowance for uncollectible accounts	80		70
PECO Energy Co [Member]
Property, Plant and Equipment, Net [Abstract]
Accumulated depreciation	3,293		3,253
Accounts receivable, net
Allowance for uncollectible accounts	72		61
Baltimore Gas and Electric Company [Member]
Property, Plant and Equipment, Net [Abstract]
Accumulated depreciation	3,311		3,254
Accounts receivable, net
Allowance for uncollectible accounts	35		32
Pepco Holdings LLC [Member] | Successor [Member]
Property, Plant and Equipment, Net [Abstract]
Accumulated depreciation	281		195
Accounts receivable, net
Allowance for uncollectible accounts	61		80
Potomac Electric Power Company [Member]
Property, Plant and Equipment, Net [Abstract]
Accumulated depreciation	3,090		3,050
Accounts receivable, net
Allowance for uncollectible accounts	18		29
Delmarva Power and Light Company [Member]
Property, Plant and Equipment, Net [Abstract]
Accumulated depreciation	1,195		1,175
Accounts receivable, net
Allowance for uncollectible accounts	20		24
Atlantic City Electric Company [Member]
Property, Plant and Equipment, Net [Abstract]
Accumulated depreciation	1,032		1,016
Accounts receivable, net
Allowance for uncollectible accounts	$ 23		$ 27

[1] Includes accumulated amortization of nuclear fuel in the reactor core of $3,171 million

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