Supplemental Financial Information - Balance Sheet (Details) (USD $) In Millions, unless otherwise specified	Sep. 30, 2014		Dec. 31, 2013
Property, Plant and Equipment, Net [Abstract]
Accumulated depreciation	$ 14,932	[1]	$ 13,713	[2]
Accounts receivable, net
Allowance for uncollectible accounts	291		272
Exelon Generation Co L L C [Member]
Property, Plant and Equipment, Net [Abstract]
Accumulated depreciation	7,868	[1]	7,034	[2]
Accounts receivable, net
Allowance for uncollectible accounts	55		57
Accumulated amortization of nuclear fuel	2,729		2,371
Commonwealth Edison Co [Member]
Property, Plant and Equipment, Net [Abstract]
Accumulated depreciation	3,370		3,184
Accounts receivable, net
Allowance for uncollectible accounts	80		62
PECO Energy Co [Member]
Property, Plant and Equipment, Net [Abstract]
Accumulated depreciation	2,972		2,935
Accounts receivable, net
Allowance for uncollectible accounts	115		107
Baltimore Gas and Electric Company [Member]
Property, Plant and Equipment, Net [Abstract]
Accumulated depreciation	2,825		2,702
Accounts receivable, net
Allowance for uncollectible accounts	$ 41		$ 46

[1] Includes accumulated amortization of nuclear fuel in the reactor core of $2,729 million.

[2] Includes accumulated amortization of nuclear fuel in the reactor core of $2,371 million.