Severance - Severance Liabilities Rollforward (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013		Dec. 31, 2012
Restructuring Cost and Reserve [Line Items]
Severance benefit obligation - beginning balance	$ 53	$ 111
Stock compensation				7	[1],[2]
Payments	(41)	(64)
Severance benefit obligation - ending balance	12	53		111
Severance [Member]
Restructuring Cost and Reserve [Line Items]
Severance charges		5	[3]
Stock Compensation Plan [Member]
Restructuring Cost and Reserve [Line Items]
Stock compensation		1
Exelon Generation Co L L C [Member]
Restructuring Cost and Reserve [Line Items]
Severance benefit obligation - beginning balance	10	33
Stock compensation				4	[1]
Payments	(7)	(24)
Severance benefit obligation - ending balance	3	10		33
Exelon Generation Co L L C [Member] | Severance [Member]
Restructuring Cost and Reserve [Line Items]
Severance charges		1	[3]
Exelon Generation Co L L C [Member] | Stock Compensation Plan [Member]
Restructuring Cost and Reserve [Line Items]
Stock compensation		0
Commonwealth Edison Co [Member]
Restructuring Cost and Reserve [Line Items]
Severance benefit obligation - beginning balance	0	1
Stock compensation				1	[1],[2]
Payments	0	(1)
Severance benefit obligation - ending balance	0	0		1
Commonwealth Edison Co [Member] | Severance [Member]
Restructuring Cost and Reserve [Line Items]
Severance charges		0	[3]
Commonwealth Edison Co [Member] | Stock Compensation Plan [Member]
Restructuring Cost and Reserve [Line Items]
Stock compensation		0
PECO Energy Co [Member]
Restructuring Cost and Reserve [Line Items]
Severance benefit obligation - beginning balance	0	0
Stock compensation				0	[1]
Payments	0	0
Severance benefit obligation - ending balance	0	0		0
PECO Energy Co [Member] | Severance [Member]
Restructuring Cost and Reserve [Line Items]
Severance charges		0	[3]
PECO Energy Co [Member] | Stock Compensation Plan [Member]
Restructuring Cost and Reserve [Line Items]
Stock compensation		0
Baltimore Gas and Electric Company [Member]
Restructuring Cost and Reserve [Line Items]
Severance benefit obligation - beginning balance	6	11
Stock compensation				1	[1],[2]
Payments	(4)	(5)
Severance benefit obligation - ending balance	2	6		11
Baltimore Gas and Electric Company [Member] | Severance [Member]
Restructuring Cost and Reserve [Line Items]
Severance charges		0	[3]
Baltimore Gas and Electric Company [Member] | Stock Compensation Plan [Member]
Restructuring Cost and Reserve [Line Items]
Stock compensation		$ 0

[1] The amounts above include $46 million at Generation, $14 million at ComEd, $7 million at PECO, and $7 million at BGE, for amounts billed by BSC through intercompany allocations for the year ended December 31, 2012.

[2] Exelon, ComEd and BGE established regulatory assets of $35 million, $16 million and $19 million, respectively, for severance benefits costs for the year ended December 31, 2012. The majority of these costs are expected to be recovered over a five-year period.

[3] Includes salary continuance and health and welfare severance benefits. Amounts primarily represent benefits provided for under Exelon’s ongoing severance plan. One-time termination benefits were not material for the years ended December 31, 2014 and December 31, 2013.