Supplemental Financial Information - Balance Sheet (Details) (USD $)	12 Months Ended
	Dec. 31, 2010	Sep. 30, 2013		Dec. 31, 2012
Supplemental Financial Information Textuals [Abstract]
Payment to IRS	$ 302,000,000
Capital Leases, Net Investment in Direct Financing Leases [Abstract]
Estimated residual value of leased assets		1,600,000,000
Accrued Liabilities Current [Abstract]
Total accrued expenses		1,540,000,000		1,800,000,000
Property, Plant And Equipment [Abstract]
Accumulated depreciation		13,366,000,000	[1]	12,184,000,000	[2]
Accumulated amortization of nuclear fuel		2,365,000,000		2,078,000,000
Accounts receivable, net
Allowance for uncollectible accounts		302,000,000		293,000,000
Accumulated Other Comprehensive Income (Loss) [Abstract]
Accumulated other comprehensive income (loss), net		(2,661,000,000)	[3]	(2,767,000,000)	[3]
Exelon Generation Co L L C [Member]
Accrued Liabilities Current [Abstract]
Total accrued expenses		925,000,000		1,116,000,000
Property, Plant And Equipment [Abstract]
Accumulated depreciation		6,848,000,000	[1]	6,014,000,000	[2]
Accumulated amortization of nuclear fuel		2,365,000,000		2,078,000,000
Accounts receivable, net
Allowance for uncollectible accounts		72,000,000		84,000,000
Accumulated Other Comprehensive Income (Loss) [Abstract]
Accumulated other comprehensive income (loss), net		243,000,000	[3]	513,000,000	[3]
Commonwealth Edison Co [Member]
Accrued Liabilities Current [Abstract]
Total accrued expenses		238,000,000		295,000,000
Property, Plant And Equipment [Abstract]
Accumulated depreciation		3,107,000,000		2,998,000,000
Accounts receivable, net
Allowance for uncollectible accounts		73,000,000		70,000,000
Accumulated Other Comprehensive Income (Loss) [Abstract]
Accumulated other comprehensive income (loss), net		0		0
PECO Energy Co [Member]
Accrued Liabilities Current [Abstract]
Total accrued expenses		91,000,000		82,000,000
Financing Receivable Recorded Investment [Line Items]
Installment plan receivables		22,000,000		18,000,000
Installment plan receivables uncollectible accounts reserve		(22,000,000)		(15,000,000)
Property, Plant And Equipment [Abstract]
Accumulated depreciation		2,914,000,000		2,797,000,000
Accounts receivable, net
Allowance for uncollectible accounts		119,000,000		99,000,000
Accumulated Other Comprehensive Income (Loss) [Abstract]
Accumulated other comprehensive income (loss), net		1,000,000	[3]	1,000,000	[3]
PECO Energy Co [Member] | Low To Medium Risk [Member]
Financing Receivable Recorded Investment [Line Items]
Installment plan receivables uncollectible accounts reserve		(1,000,000)		(1,000,000)
PECO Energy Co [Member] | Medium Risk [Member]
Financing Receivable Recorded Investment [Line Items]
Installment plan receivables uncollectible accounts reserve		(4,000,000)		(3,000,000)
PECO Energy Co [Member] | High Risk [Member]
Financing Receivable Recorded Investment [Line Items]
Installment plan receivables uncollectible accounts reserve		(17,000,000)		(11,000,000)
Baltimore Gas and Electric Company [Member]
Accrued Liabilities Current [Abstract]
Total accrued expenses		127,000,000		106,000,000
Property, Plant And Equipment [Abstract]
Accumulated depreciation		2,658,000,000		2,595,000,000
Accounts receivable, net
Allowance for uncollectible accounts		$ 38,000,000		$ 40,000,000

[1] Includes accumulated amortization of nuclear fuel in the reactor core of $2,365 million.

[2] Includes accumulated amortization of nuclear fuel in the reactor core of $2,078 million.

[3] (a) All amounts are net of tax. Amounts in parenthesis represent a decrease in accumulated other comprehensive income.