Supplemental Financial Information - Balance Sheet (Details) (USD $) In Millions, unless otherwise specified	Mar. 31, 2015		Dec. 31, 2014
Property, Plant and Equipment, Net [Abstract]
Accumulated depreciation	$ 15,207	[1]	$ 14,742	[2]
Accounts receivable, net
Allowance for uncollectible accounts	365		311
Exelon Generation Co L L C [Member]
Property, Plant and Equipment, Net [Abstract]
Accumulated depreciation	7,905	[1]	7,612	[2]
Accounts receivable, net
Allowance for uncollectible accounts	61		60
Accumulated amortization of nuclear fuel	2,772		2,673
Commonwealth Edison Co [Member]
Property, Plant and Equipment, Net [Abstract]
Accumulated depreciation	3,247		3,432
Accounts receivable, net
Allowance for uncollectible accounts	100		84
PECO Energy Co [Member]
Property, Plant and Equipment, Net [Abstract]
Accumulated depreciation	2,989		2,917
Accounts receivable, net
Allowance for uncollectible accounts	127		100
Baltimore Gas and Electric Company [Member]
Property, Plant and Equipment, Net [Abstract]
Accumulated depreciation	2,905		2,868
Accounts receivable, net
Allowance for uncollectible accounts	$ 84		$ 67

[1] Includes accumulated amortization of nuclear fuel in the reactor core of $2,772 million.

[2] Includes accumulated amortization of nuclear fuel in the reactor core of $2,673 million.