Supplemental Financial Information - Balance Sheet (Details) - USD ($) $ in Millions	Sep. 30, 2016		Dec. 31, 2015
Property, Plant and Equipment, Net [Abstract]
Accumulated depreciation	$ 18,354	[1]	$ 16,375	[2]
Accounts receivable, net
Allowance for uncollectible accounts	330		284
Exelon Generation Co L L C [Member]
Property, Plant and Equipment, Net [Abstract]
Accumulated depreciation	10,004	[1]	8,639	[2]
Accounts receivable, net
Allowance for uncollectible accounts	85		77
Exelon Generation Co L L C [Member] | Nuclear Fuel [Member]
Property, Plant and Equipment, Net [Abstract]
Accumulated depreciation	3,198		2,861
Commonwealth Edison Co [Member]
Property, Plant and Equipment, Net [Abstract]
Accumulated depreciation	3,841		3,710
Accounts receivable, net
Allowance for uncollectible accounts	82		75
PECO Energy Co [Member]
Property, Plant and Equipment, Net [Abstract]
Accumulated depreciation	3,213		3,101
Accounts receivable, net
Allowance for uncollectible accounts	78		83
Baltimore Gas and Electric Company [Member]
Property, Plant and Equipment, Net [Abstract]
Accumulated depreciation	3,198		3,016
Accounts receivable, net
Allowance for uncollectible accounts	39		49
Pepco Holdings LLC [Member] | Predecessor [Member]
Property, Plant and Equipment, Net [Abstract]
Accumulated depreciation			5,341
Accounts receivable, net
Allowance for uncollectible accounts			56
Pepco Holdings LLC [Member] | Successor [Member]
Property, Plant and Equipment, Net [Abstract]
Accumulated depreciation	146
Accounts receivable, net
Allowance for uncollectible accounts	46
Potomac Electric Power Company [Member]
Property, Plant and Equipment, Net [Abstract]
Accumulated depreciation	3,026		2,929
Accounts receivable, net
Allowance for uncollectible accounts	15		17
Delmarva Power and Light Company [Member]
Property, Plant and Equipment, Net [Abstract]
Accumulated depreciation	1,171		1,139
Accounts receivable, net
Allowance for uncollectible accounts	14		17
Atlantic City Electric Company [Member]
Property, Plant and Equipment, Net [Abstract]
Accumulated depreciation	1,008		968
Accounts receivable, net
Allowance for uncollectible accounts	$ 17		$ 17

[1] Includes accumulated amortization of nuclear fuel in the reactor core of $3,198 million

[2] Includes accumulated amortization of nuclear fuel in the reactor core of $2,861 million