Supplemental Financial Information - Balance Sheet (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2010	Mar. 31, 2013		Dec. 31, 2012
Supplemental Financial Information Textuals [Abstract]
Payment to IRS	$ 302
Accrued Liabilities Current [Abstract]
Total accrued expenses		1,430		1,800
Property, Plant And Equipment [Abstract]
Accumulated depreciation		12,579	[1]	12,184	[2]
Accumulated amortization of nuclear fuel		2,221		2,078
Accounts receivable, net
Allowance for uncollectible accounts		(320)		(293)
Accumulated Other Comprehensive Income (Loss) [Abstract]
Accumulated other comprehensive income (loss), net		(2,673)	[3]	(2,767)	[3]
Exelon Generation Co L L C [Member]
Capital Leases, Net Investment in Direct Financing Leases [Abstract]
Net investment in long-term leases		700
Accrued Liabilities Current [Abstract]
Total accrued expenses		904		1,116
Property, Plant And Equipment [Abstract]
Accumulated depreciation		6,347	[1]	6,014	[2]
Accumulated amortization of nuclear fuel		2,221		2,078
Accounts receivable, net
Allowance for uncollectible accounts		(84)		(84)
Accumulated Other Comprehensive Income (Loss) [Abstract]
Accumulated other comprehensive income (loss), net		409	[3]	513	[3]
Commonwealth Edison Co [Member]
Accrued Liabilities Current [Abstract]
Total accrued expenses		199		295
Property, Plant And Equipment [Abstract]
Accumulated depreciation		2,969		2,998
Accounts receivable, net
Allowance for uncollectible accounts		(78)		(70)
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		97		82
Financing Receivable Recorded Investment [Line Items]
Installment plan receivables		18
Installment plan receivables uncollectible accounts reserve		(14)		(15)
Property, Plant And Equipment [Abstract]
Accumulated depreciation		2,840		2,797
Accounts receivable, net
Allowance for uncollectible accounts		(122)		(99)
Accumulated Other Comprehensive Income (Loss) [Abstract]
Accumulated other comprehensive income (loss), net		1	[3]	1	[3]
PECO Energy Co [Member] | Low To Medium Risk [Member]
Financing Receivable Recorded Investment [Line Items]
Installment plan receivables uncollectible accounts reserve		(1)		(1)
PECO Energy Co [Member] | Medium Risk [Member]
Financing Receivable Recorded Investment [Line Items]
Installment plan receivables uncollectible accounts reserve		(4)		(3)
PECO Energy Co [Member] | High Risk [Member]
Financing Receivable Recorded Investment [Line Items]
Installment plan receivables uncollectible accounts reserve		(9)		(11)
Baltimore Gas and Electric Company [Member]
Accrued Liabilities Current [Abstract]
Total accrued expenses		100		106
Property, Plant And Equipment [Abstract]
Accumulated depreciation		2,627		2,595
Accounts receivable, net
Allowance for uncollectible accounts		$ (36)		$ (40)

[1] Includes accumulated amortization of nuclear fuel in the reactor core of $2,221 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.