Supplemental Financial Information - Balance Sheet (Details) - USD ($) $ in Millions	Sep. 30, 2017		Dec. 31, 2016
Property, Plant and Equipment, Net [Abstract]
Accumulated depreciation	$ 20,591	[1]	$ 19,169	[2]
Accounts receivable, net
Allowance for uncollectible accounts	339		334
Exelon Generation Co L L C [Member]
Property, Plant and Equipment, Net [Abstract]
Accumulated depreciation	11,193	[1]	10,562	[2]
Accounts receivable, net
Allowance for uncollectible accounts	111		91
Exelon Generation Co L L C [Member] | Nuclear Fuel [Member]
Property, Plant and Equipment, Net [Abstract]
Accumulated depreciation	3,303		3,186
Commonwealth Edison Co [Member]
Property, Plant and Equipment, Net [Abstract]
Accumulated depreciation	4,191		3,937
Accounts receivable, net
Allowance for uncollectible accounts	72		70
PECO Energy Co [Member]
Property, Plant and Equipment, Net [Abstract]
Accumulated depreciation	3,366		3,253
Accounts receivable, net
Allowance for uncollectible accounts	57		61
Baltimore Gas and Electric Company [Member]
Property, Plant and Equipment, Net [Abstract]
Accumulated depreciation	3,351		3,254
Accounts receivable, net
Allowance for uncollectible accounts	25		32
Pepco Holdings LLC [Member] | Successor [Member]
Property, Plant and Equipment, Net [Abstract]
Accumulated depreciation	448		195
Accounts receivable, net
Allowance for uncollectible accounts	74		80
Potomac Electric Power Company [Member]
Property, Plant and Equipment, Net [Abstract]
Accumulated depreciation	3,171		3,050
Accounts receivable, net
Allowance for uncollectible accounts	29		29
Delmarva Power and Light Company [Member]
Property, Plant and Equipment, Net [Abstract]
Accumulated depreciation	1,231		1,175
Accounts receivable, net
Allowance for uncollectible accounts	17		24
Atlantic City Electric Company [Member]
Property, Plant and Equipment, Net [Abstract]
Accumulated depreciation	1,060		1,016
Accounts receivable, net
Allowance for uncollectible accounts	$ 28		$ 27

[1] Includes accumulated amortization of nuclear fuel in the reactor core of $3,303 million

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