Stock-Based Compensation Plans (Details) (USD $) In Millions, except Share data, unless otherwise specified	3 Months Ended		9 Months Ended			9 Months Ended	12 Months Ended	3 Months Ended		9 Months Ended		3 Months Ended		9 Months Ended		3 Months Ended		9 Months Ended		3 Months Ended				9 Months Ended				3 Months Ended				9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012	Dec. 31, 2012	Sep. 30, 2013 Performance Share Awards [Member]	Dec. 31, 2012 Performance Share Awards [Member]	Sep. 30, 2013 Exelon Generation Co L L C [Member]	Sep. 30, 2012 Exelon Generation Co L L C [Member]	Sep. 30, 2013 Exelon Generation Co L L C [Member]	Sep. 30, 2012 Exelon Generation Co L L C [Member]	Sep. 30, 2013 Commonwealth Edison Co [Member]	Sep. 30, 2012 Commonwealth Edison Co [Member]	Sep. 30, 2013 Commonwealth Edison Co [Member]	Sep. 30, 2012 Commonwealth Edison Co [Member]	Sep. 30, 2013 PECO Energy Co [Member]	Sep. 30, 2012 PECO Energy Co [Member]	Sep. 30, 2013 PECO Energy Co [Member]	Sep. 30, 2012 PECO Energy Co [Member]	Sep. 30, 2013 Baltimore Gas and Electric Company [Member]		Sep. 30, 2012 Baltimore Gas and Electric Company [Member]		Sep. 30, 2013 Baltimore Gas and Electric Company [Member]		Sep. 30, 2012 Baltimore Gas and Electric Company [Member]		Sep. 30, 2013 Business Services Company [Member]		Sep. 30, 2012 Business Services Company [Member]		Sep. 30, 2013 Business Services Company [Member]		Sep. 30, 2012 Business Services Company [Member]
Common Stock [Abstract]
Common Stock without par - Authorized	2,000,000,000		2,000,000,000		2,000,000,000
Common Stock without par - Outstanding	856,563,385		856,563,385		855,000,000
Authorized Shares for LTIP [Abstract]
Authorized Shares for LTIP	16,000,000		16,000,000
Share Based Compensation Components [Abstract]
Performance shares	$ 12	$ 5	$ 41	$ 32
Stock options	1	2	3	13
Restricted stock units	13	12	49	41
Other stock-based awards	1	1	4	3
Total stock-based compensation included in operating and maintenance expense	27	20	97	89
Income Tax Benefit	(10)	(8)	(37)	(34)
Total after-tax stock based compensation expense	17	12	60	55
Share Based Compensation Pre Tax Expense [Line Items]
Pre-tax stock based compensation expense	27	20	97	89				10	9	38	33	3	2	7	9	1	1	4	4	1	[1]	1	[1]	5	[1]	4	[1]	12	[2]	7	[2]	43	[2],[3]	39	[2],[3]
Share Based Compensation Arrangement By Share Based Payment Award Equity Instruments Other Than Options Nonvested Roll Forward
Expected Payout Minimum						50.00%	75.00%
Expected Payout Maximum						150.00%	125.00%
Additional Information Regarding Stock Options Exercised [Abstract]
Unrecognized compensation costs related to nonvested stock options	3		3
Weighted Average Period Non Vested Stock Options Are Expected To Be Recognized Over	1 year 9 months 22 days		1 year 9 months 22 days
Restricted Stock Units [Abstract]
Obligations related to outstanding restricted stock units not yet settled	67		67		58
Obligations related to outstanding restricted stock units that will be settled in cash	0		0
Fair value of settled restricted stock	3	4	26	23
Unrecognized compensation costs related to nonvested restricted stock units	69		69
Weighted average period	2 years 2 months 13 days		2 years 2 months 13 days
Performance Share Awards [Abstract]
Percentage of current performance share awards settled in stock			50.00%
Percentage of current performance share awards settled in cash			50.00%
Percentage of current performance share awards settled in cash for executive vice presidents and higher officers			100.00%
Expected TSR Percentage Increase			25.00%
Expected TSR Percentage Decrease			25.00%
Expected IPM Percentage Decrease			50.00%
Expected IPM Percentage Increase			20.00%
Expected IPM Percentage Increase for Senior VPs and above			10.00%
Performance shares settled at fair value of	3	3	25	22
Performance shares settled at fair value and paid with cash	3	0	12	3
Unrecognized compensation costs related to nonvested performance shares	32		32
Weighted average period	2 years 3 months 19 days		2 years 3 months 19 days
Obligation Related To Outstanding Performance Share Awards [Abstract]
Total	63		63		53
Performance Share Transition Awards [Abstract]
Unrecognized compensation costs related to nonvested performance shares transition	$ 19		$ 19
Weighted average period	1 year 3 months 20 days		1 year 3 months 20 days

[1] BGE's stock-based compensation expense (pre-tax) for the nine months ended September 30, 2012 excludes $2 million of cost incurred in 2012 prior to the closing of Exelon's merger with Constellation on March 12, 2012. This amount is not included in Exelon's stock-based compensation expense for the nine months ended September 30, 2012 shown in the tables titled Components of Stock-Based Compensation Expense and Subsidiaries above.

[2] These amounts primarily represent amounts billed to Exelon's subsidiaries through intercompany allocations. These amounts are not included in the Generation, ComEd, PECO and BGE amounts above.

[3] These amounts primarily represent amounts billed to Exelon?s subsidiaries through intercompany allocations. These amounts are not included in the Generation, ComEd, PECO and BGE amounts above.