Supplemental Financial Information - Balance Sheet (Details) (USD $)	12 Months Ended
	Dec. 31, 2010	Jun. 30, 2012		Dec. 31, 2011
Supplemental Financial Information Textuals [Abstract]
Payment to IRS	$ 302,000,000
Accrued Liabilities Current [Abstract]
Total accrued expenses		1,452,000,000		1,255,000,000
Property, Plant And Equipment [Abstract]
Accumulated depreciation		11,367,000,000	[1]	10,959,000,000	[2]
Accumulated amortization of nuclear fuel		1,951,000,000		1,784,000,000
Accounts receivable, net
Allowance for uncollectible accounts		(303,000,000)		(199,000,000)
Accumulated Other Comprehensive Income (Loss) [Abstract]
Net unrealized gain (loss) on cash flow hedges		547,000,000		488,000,000
Pension and non-pension postretirement benefit plans		(2,864,000,000)		(2,938,000,000)
Net unrealized losses on foreign currency translation		(2,000,000)
Other comprehensive loss equity investment in CENG		6,000,000
Accumulated unrealized gain (loss) on marketable securities		0
Accumulated other comprehensive income (loss), net		(2,313,000,000)		(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		670,000,000
Accrued Liabilities Current [Abstract]
Total accrued expenses		885,000,000		779,000,000
Property, Plant And Equipment [Abstract]
Accumulated depreciation		5,526,000,000	[1]	5,313,000,000	[2]
Accumulated amortization of nuclear fuel		1,951,000,000		1,784,000,000
Accounts receivable, net
Allowance for uncollectible accounts		(91,000,000)		(29,000,000)
Accumulated Other Comprehensive Income (Loss) [Abstract]
Net unrealized gain (loss) on cash flow hedges		901,000,000		915,000,000
Net unrealized losses on foreign currency translation		(2,000,000)
Other comprehensive loss equity investment in CENG		6,000,000
Accumulated unrealized gain (loss) on marketable securities		(1,000,000)
Accumulated other comprehensive income (loss), net		904,000,000		915,000,000
Commonwealth Edison Co [Member]
Accrued Liabilities Current [Abstract]
Total accrued expenses		244,000,000		318,000,000
Property, Plant And Equipment [Abstract]
Accumulated depreciation		2,844,000,000		2,750,000,000
Accounts receivable, net
Allowance for uncollectible accounts		(78,000,000)		(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		71,000,000		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		2,731,000,000		2,662,000,000
Accounts receivable, net
Allowance for uncollectible accounts		(102,000,000)		(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		110,000,000		148,000,000
Property, Plant And Equipment [Abstract]
Accumulated depreciation		2,549,000,000		2,465,000,000
Accounts receivable, net
Allowance for uncollectible accounts		(32,000,000)		(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 $1,951 million.

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