Severance - Ongoing Severance Plans (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2014		Dec. 31, 2013		Dec. 31, 2012
Other Severance Charges [Member]
Restructuring Cost and Reserve [Line Items]
Severance charges	$ 7	[1]	$ 18	[1]	$ 19	[1]
Business Service Company [Member]
Restructuring Cost and Reserve [Line Items]
Severance charges			2		0
Severance [Member]
Restructuring Cost and Reserve [Line Items]
Severance charges	3
Severance accrual	3
Exelon Generation Co L L C [Member] | Other Severance Charges [Member]
Restructuring Cost and Reserve [Line Items]
Severance charges	5	[1]	16	[1]	14	[1]
Exelon Generation Co L L C [Member] | Business Service Company [Member]
Restructuring Cost and Reserve [Line Items]
Severance charges	1
Commonwealth Edison Co [Member] | Other Severance Charges [Member]
Restructuring Cost and Reserve [Line Items]
Severance charges	1	[1]	2	[1]	2	[1]
PECO Energy Co [Member] | Other Severance Charges [Member]
Restructuring Cost and Reserve [Line Items]
Severance charges	0	[1]	0	[1]	1	[1]
Baltimore Gas and Electric Company [Member] | Other Severance Charges [Member]
Restructuring Cost and Reserve [Line Items]
Severance charges	$ 1	[1]	$ 0	[1]	$ 3	[1]

[1] The amounts above for Generation include $1 million, $2 million, and $0 million for amounts billed by BSC through intercompany allocations for the years ended December 31, 2014, December 31, 2013, and December 31, 2012, respectively. Amounts billed by BSC to ComEd, PECO and BGE were not material