Accounts Receivable (Details) (USD $)	Mar. 31, 2012	Dec. 31, 2011	Sep. 30, 2011	Dec. 31, 2010
Accounts Notes And Loans Receivable Net Current [Abstract]
Allowance for uncollectible accounts	$ (317,000,000)	$ (199,000,000)
Accounts Receivable Additional Disclosures [Abstract]
Accounts receivable, pledged under accounts receivable agreement			225,000,000	225,000,000
Gross Accounts Receivable Pledged as Collateral	348,000,000	329,000,000	348,000,000	329,000,000
Exelon Generation Co L L C [Member]
Accounts Notes And Loans Receivable Net Current [Abstract]
Allowance for uncollectible accounts	(82,000,000)	(29,000,000)
Commonwealth Edison Co [Member]
Accounts Notes And Loans Receivable Net Current [Abstract]
Allowance for uncollectible accounts	(90,000,000)	(78,000,000)
PECO Energy Co [Member]
Accounts Notes And Loans Receivable Net Current [Abstract]
Allowance for uncollectible accounts	(111,000,000)	(92,000,000)
Accounts Receivable Additional Disclosures [Abstract]
Accounts receivable, pledged under accounts receivable agreement			225,000,000	225,000,000
Gross Accounts Receivable Pledged as Collateral	348,000,000	329,000,000	348,000,000	329,000,000
Financing Receivable Recorded Investment [Line Items]
Installment plan receivables	17,000,000	21,000,000
Installment plan receivables uncollectible accounts reserve	(13,000,000)	(17,000,000)
PECO Energy Co [Member] | Low Risk [Member]
Financing Receivable Recorded Investment [Line Items]
Installment plan receivables uncollectible accounts reserve	0	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	(8,000,000)	(13,000,000)
Baltimore Gas and Electric Company [Member]
Accounts Notes And Loans Receivable Net Current [Abstract]
Allowance for uncollectible accounts	$ (34,000,000)	$ (38,000,000)