Supplemental Financial Information - Balance Sheet (Details) (USD $)	12 Months Ended
	Dec. 31, 2010	Sep. 30, 2012		Dec. 31, 2011
Supplemental Financial Information Textuals [Abstract]
Payment to IRS	$ 302,000,000
Accrued Liabilities Current [Abstract]
Total accrued expenses		1,502,000,000		1,255,000,000
Property, Plant And Equipment [Abstract]
Accumulated depreciation		11,890,000,000	[1]	10,959,000,000	[2]
Accumulated amortization of nuclear fuel		2,161,000,000		1,784,000,000
Accounts receivable, net
Allowance for uncollectible accounts		(310,000,000)		(199,000,000)
Accumulated Other Comprehensive Income (Loss) [Abstract]
Net unrealized gain (loss) on cash flow hedges		459,000,000		488,000,000
Pension and non-pension postretirement benefit plans		(2,887,000,000)		(2,938,000,000)
Net unrealized losses on foreign currency translation		0
Other comprehensive loss equity investment in CENG		23,000,000
Accumulated unrealized gain (loss) on marketable securities		0
Accumulated other comprehensive income (loss), net		(2,405,000,000)		(2,450,000,000)
Exelon Generation Co L L C [Member]
Capital Leases, Net Investment in Direct Financing Leases [Abstract]
Net investment in long-term leases		678,000,000
Accrued Liabilities Current [Abstract]
Total accrued expenses		1,106,000,000		779,000,000
Property, Plant And Equipment [Abstract]
Accumulated depreciation		5,910,000,000	[1]	5,313,000,000	[2]
Accumulated amortization of nuclear fuel		2,161,000,000		1,784,000,000
Accounts receivable, net
Allowance for uncollectible accounts		(85,000,000)		(29,000,000)
Accumulated Other Comprehensive Income (Loss) [Abstract]
Net unrealized gain (loss) on cash flow hedges		730,000,000		915,000,000
Net unrealized losses on foreign currency translation		0
Other comprehensive loss equity investment in CENG		23,000,000
Accumulated unrealized gain (loss) on marketable securities		(1,000,000)
Accumulated other comprehensive income (loss), net		752,000,000		915,000,000
Commonwealth Edison Co [Member]
Accrued Liabilities Current [Abstract]
Total accrued expenses		220,000,000		318,000,000
Property, Plant And Equipment [Abstract]
Accumulated depreciation		2,906,000,000		2,750,000,000
Accounts receivable, net
Allowance for uncollectible accounts		(81,000,000)		(78,000,000)
Accumulated Other Comprehensive Income (Loss) [Abstract]
Net unrealized gain (loss) on cash flow hedges				0
Accumulated unrealized gain (loss) on marketable securities		0		(1,000,000)
Accumulated other comprehensive income (loss), net		0		(1,000,000)
PECO Energy Co [Member]
Accrued Liabilities Current [Abstract]
Total accrued expenses		87,000,000		83,000,000
Financing Receivable Recorded Investment [Line Items]
Installment plan receivables		21,000,000		21,000,000
Installment plan receivables uncollectible accounts reserve		(18,000,000)		(17,000,000)
Property, Plant And Equipment [Abstract]
Accumulated depreciation		2,765,000,000		2,662,000,000
Accounts receivable, net
Allowance for uncollectible accounts		(109,000,000)		(92,000,000)
Accumulated Other Comprehensive Income (Loss) [Abstract]
Net unrealized gain (loss) on cash flow hedges				0
Accumulated unrealized gain (loss) on marketable securities		1,000,000
Accumulated other comprehensive income (loss), net		1,000,000		0
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		(13,000,000)		(13,000,000)
Baltimore Gas and Electric Company [Member]
Accrued Liabilities Current [Abstract]
Total accrued expenses		125,000,000		148,000,000
Property, Plant And Equipment [Abstract]
Accumulated depreciation		2,579,000,000		2,465,000,000
Accounts receivable, net
Allowance for uncollectible accounts		(35,000,000)		(38,000,000)
Accumulated Other Comprehensive Income (Loss) [Abstract]
Net unrealized gain (loss) on cash flow hedges				0
Accumulated unrealized gain (loss) on marketable securities		0
Accumulated other comprehensive income (loss), net		$ 0		$ 0

[1] Includes accumulated amortization of nuclear fuel in the reactor core of $2,161 million.

[2] Includes accumulated amortization of nuclear fuel in the reactor core of $1,784 million.