Stock-Based Compensation Plans (Details) (USD $) In Millions, except Share data, unless otherwise specified	3 Months Ended		6 Months Ended			6 Months Ended	12 Months Ended	3 Months Ended		6 Months Ended		3 Months Ended		6 Months Ended		3 Months Ended		6 Months Ended		3 Months Ended				6 Months Ended				3 Months Ended				6 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013	Jun. 30, 2012	Dec. 31, 2012	Jun. 30, 2013 Performance Share Awards [Member]	Dec. 31, 2012 Performance Share Awards [Member]	Jun. 30, 2013 Exelon Generation Co L L C [Member]	Jun. 30, 2012 Exelon Generation Co L L C [Member]	Jun. 30, 2013 Exelon Generation Co L L C [Member]	Jun. 30, 2012 Exelon Generation Co L L C [Member]	Jun. 30, 2013 Commonwealth Edison Co [Member]	Jun. 30, 2012 Commonwealth Edison Co [Member]	Jun. 30, 2013 Commonwealth Edison Co [Member]	Jun. 30, 2012 Commonwealth Edison Co [Member]	Jun. 30, 2013 PECO Energy Co [Member]	Jun. 30, 2012 PECO Energy Co [Member]	Jun. 30, 2013 PECO Energy Co [Member]	Jun. 30, 2012 PECO Energy Co [Member]	Jun. 30, 2013 Baltimore Gas and Electric Company [Member]		Jun. 30, 2012 Baltimore Gas and Electric Company [Member]		Jun. 30, 2013 Baltimore Gas and Electric Company [Member]		Jun. 30, 2012 Baltimore Gas and Electric Company [Member]		Jun. 30, 2013 Business Services Company [Member]		Jun. 30, 2012 Business Services Company [Member]		Jun. 30, 2013 Business Services Company [Member]		Jun. 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	$ 13	$ 10	$ 29	$ 26
Stock options	1	4	2	11
Restricted stock units	16	11	36	30
Other stock-based awards	2	1	3	2
Total stock-based compensation included in operating and maintenance expense	32	26	70	69
Income Tax Benefit	(12)	(10)	(27)	(26)
Total after-tax stock based compensation expense	20	16	43	43
Share Based Compensation Pre Tax Expense [Line Items]
Pre-tax stock based compensation expense	32	26	70	69				13	9	28	24	2	2	4	7	1	1	3	3	2	[1]	1	[1]	4	[1]	3	[1]	14	[2]	13	[2]	31	[2],[3]	32	[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	2 years		2 years
Restricted Stock Units [Abstract]
Obligations related to outstanding restricted stock units not yet settled	60		60		58
Obligations related to outstanding restricted stock units that will be settled in cash	0		0
Fair value of settled restricted stock	1	2	23	21
Unrecognized compensation costs related to nonvested restricted stock units	81		81
Weighted average period	2 years 4 months 26 days		2 years 4 months 26 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	1	19	23	19
Performance shares settled at fair value and paid with cash	1	3	10	3
Unrecognized compensation costs related to nonvested performance shares	39		39
Weighted average period	2 years 6 months 3 days		2 years 6 months 3 days
Obligation Related To Outstanding Performance Share Awards [Abstract]
Total	54		54		53
Performance Share Transition Awards [Abstract]
Unrecognized compensation costs related to nonvested performance shares transition	$ 25		$ 25
Weighted average period	1 year 7 months 9 days		1 year 7 months 9 days

[1] BGE's stock-based compensation expense (pre-tax) for the six months ended June 30, 2012 includes $2 million of cost incurred 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 six months ended June 30, 2012 shown in the table titled Components of Stock-Based Compensation Expense 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.