Supplemental Financial Information - Balance Sheet (Details) - USD ($) $ in Millions		9 Months Ended		12 Months Ended
		Sep. 30, 2015		Dec. 31, 2014
Property, Plant and Equipment, Net [Abstract]
Accumulated depreciation		$ 16,185	[1]	$ 14,742	[2]
Accounts receivable, net
Allowance for uncollectible accounts		329		311
Exelon Generation Co L L C [Member]
Property, Plant and Equipment, Net [Abstract]
Accumulated depreciation		8,659	[1]	7,612	[2]
Accounts receivable, net
Allowance for uncollectible accounts		70		60
Accumulated amortization of nuclear fuel		3,093		2,673
Commonwealth Edison Co [Member]
Property, Plant and Equipment, Net [Abstract]
Accumulated depreciation		3,614		3,432
Accounts receivable, net
Allowance for uncollectible accounts		100		84
PECO Energy Co [Member]
Property, Plant and Equipment, Net [Abstract]
Accumulated depreciation		3,058		2,917
Accounts receivable, net
Allowance for uncollectible accounts	[3]	98		100
Financing Receivable, Allowance for Credit Losses		17		15
CurrentFinancingReceivableAllowanceForCreditLosses		9		7
Baltimore Gas and Electric Company [Member]
Property, Plant and Equipment, Net [Abstract]
Accumulated depreciation		2,962		2,868
Accounts receivable, net
Allowance for uncollectible accounts		$ 61		$ 67

[1] Includes accumulated amortization of nuclear fuel in the reactor core of $3,093 million.

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

[3] Excludes the non-current allowance for uncollectible accounts related to PECO's installment plan receivables described below of $9 million and $7 million at September 30, 2015 and December 31, 2014, respectively.