Accounts Receivable (Details) (USD $) In Millions, unless otherwise specified	Sep. 30, 2013	Dec. 31, 2012
Accounts Notes And Loans Receivable Net Current [Abstract]
Allowance for uncollectible accounts	$ 302	$ 293
Accounts Receivable Additional Disclosures [Abstract]
Gross Accounts Receivable Pledged as Collateral	0	289
Exelon Generation Co L L C [Member]
Accounts Notes And Loans Receivable Net Current [Abstract]
Allowance for uncollectible accounts	72	84
Commonwealth Edison Co [Member]
Accounts Notes And Loans Receivable Net Current [Abstract]
Allowance for uncollectible accounts	73	70
PECO Energy Co [Member]
Accounts Notes And Loans Receivable Net Current [Abstract]
Allowance for uncollectible accounts	119	99
Accounts Receivable Additional Disclosures [Abstract]
Gross Accounts Receivable Pledged as Collateral		289
Financing Receivable Recorded Investment [Line Items]
Installment plan receivables	22	18
Installment plan receivables uncollectible accounts reserve	(22)	(15)
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	(17)	(11)
Baltimore Gas and Electric Company [Member]
Accounts Notes And Loans Receivable Net Current [Abstract]
Allowance for uncollectible accounts	$ 38	$ 40