Stock-Based Compensation Plans (Details) (USD $)	3 Months Ended			3 Months Ended					3 Months Ended			3 Months Ended
	Mar. 31, 2012 Years	Mar. 31, 2011 Years	Dec. 31, 2011	Mar. 31, 2012 Stock Options [Member]		Mar. 31, 2012 Nonvested Stock Option [Member]		Dec. 31, 2011 Nonvested Stock Option [Member]	Mar. 31, 2012 Restricted Stock [Member]		Dec. 31, 2011 Restricted Stock [Member]	Mar. 31, 2012 Performance Share Awards [Member]		Dec. 31, 2011 Performance Share Awards [Member]	Mar. 31, 2012 Exelon Generation Co L L C [Member]	Mar. 31, 2011 Exelon Generation Co L L C [Member]	Mar. 31, 2012 Commonwealth Edison Co [Member]	Mar. 31, 2011 Commonwealth Edison Co [Member]	Mar. 31, 2012 PECO Energy Co [Member]	Mar. 31, 2011 PECO Energy Co [Member]	Mar. 31, 2012 Baltimore Gas and Electric Company [Member]		Mar. 11, 2012 Baltimore Gas and Electric Company [Member]	Mar. 31, 2011 Baltimore Gas and Electric Company [Member]	Mar. 31, 2012 Business Services Company [Member]		Mar. 31, 2011 Business Services Company [Member]
Common Stock [Abstract]
Common Stock without par - Authorized	2,000,000,000		2,000,000,000
Common Stock without par - Outstanding	852,000,000		663,000,000
Authorized Shares for LTIP [Abstract]
Authorized Shares for LTIP	21,000,000
Share Based Compensation Components [Abstract]
Performance shares	$ 16,000,000	$ 6,000,000
Stock options	7,000,000	5,000,000
Restricted stock units	19,000,000	16,000,000
Other stock-based awards	1,000,000	1,000,000
Total stock-based compensation included in operating and maintenance expense	43,000,000	28,000,000
Income Tax Benefit	(16,000,000)	(11,000,000)
Total after-tax stock based compensation expense	27,000,000	17,000,000
Share Based Compensation Pre Tax Expense [Line Items]
Pre-tax stock based compensation expense	43,000,000	28,000,000													14,000,000	13,000,000	5,000,000	2,000,000	3,000,000	2,000,000	2,000,000	[1]	2,000,000	2,000,000	19,000,000	[2]	11,000,000	[2]
Share Based Compensation Arrangement By Share Based Payment Award Options Outstanding Roll Forward
Shares outstanding, beginning balance - shares				11,553,761		877,050	[3]
Granted - shares				1,840,000		1,840,000	[4]
Converted Options Acquiree				11,194,151		11,194,151
Exercised - shares				(237,490)
Vested - shares						(10,969,509)	[4],[5]
Forfeited - shares				(4,625)		(70,098)
Expired - shares				(70,098)
Shares outstanding, ending balance - shares				24,275,699		2,871,594	[3]
Exercisable stock options - shares				21,404,105	[6]
Shares outstanding, beginning balance - weighted average exercise price (per share)				$ 48.49		$ 48.66
Granted - weighted average exercise price (per share)				$ 39.79		$ 39.79
Converted options of acquiree				$ 41.35		$ 41.35			$ 38.91
Exercised - weighted average exercise price (per share)				$ 25.29
Vested - weighted average exercise price (per share)						$ 41.85
Forfeited - weighted average exercise price (per share)				$ 53.51		$ 45.28
Expired - weighted average exercise price (per share)				$ 45.28
Shares outstanding, ending balance - weighted average exercise price (per share)				$ 44.78
Exercisable stock options - weighted average exercise price (per share)				$ 45.33
Share Based Compensation Arrangement By Share Based Payment Award Equity Instruments Other Than Options Nonvested Roll Forward
Equity instruments other than options - shares, beginning balance									1,074,484	[7]		346,848	[8]
Granted - shares									1,035,280			1,036,603
Vested - shares									(292,923)			(151,700)
Forfeited - shares									(10,784)			(2,183)
Undistributed Vested Awards - shares									(518,064)	[9]		(172,991)	[10]
Equity instruments other than options - shares, ending balance									2,113,728	[7]		1,056,577	[8]
Equity instruments other than options - Weighted average grant date fair value (per share), beginning balance									$ 48.08			$ 45.37
Granted - Weighted average grant date fair value (per share)									$ 39.81			$ 39.84
Vested - Weighted average grant date fair value (per share)									$ 47.71			$ 47.87
Forfeited - Weighted average grant date fair value (per share)									$ 44.63			$ 43.40
Undistributed Vested Awards - weighted average exercise price (per share)									$ 39.68			$ 40.37
Equity instruments other than options - Weighted average grant date fair value (per share), ending balance						$ 40.58			$ 42.57			$ 40.41
Stock Based Compensation Other Than Options Converted Acquiree	825,735
Expected Payout Minimum												75.00%
Expected Payout Maximum												125.00%
Schedule Of Share Based Compensation Arrangements By Share Based Payment Award Footnotes To Table [Abstract]
Fully vested stock based compensation issued to retirement-eligible employees						2,141,000		1,348,000	610,398		448,827	274,813		455,418
Stock based compensation issued to retirement eligible employees that vested immediately on the date of the grant.						1,013,000
Share Based Compensation Acquisition Arrangement [Abstract]
Fair value of stock based compensation used of acquiree	71,000,000
Stock based compensation of acquiree converted	12,037,093
Value of stock based compensation converted				65,000,000
No Sale Restricted Stock Converted Shares	165,219								153,654
No Sale Restricted Stock Converted Value									6,000,000
Fair value of each option estimated using the Black-Scholes-Merton option-pricing model
Dividend yield	0.0528%	0.0484%
Expected volatility	0.232%	0.244%
Risk-free interest rate	0.013%	0.0265%
Expected life (years)	6.25	6.25
Additional Information Regarding Stock Options Exercised [Abstract]
Unrecognized compensation costs related to nonvested stock options	14,000,000
Weighted Average Period Non Vested Stock Options Are Expected To Be Recognized Over	3.10
Restricted Stock Units [Abstract]
Obligations related to outstanding restricted stock units not yet settled	47,000,000
Obligations related to outstanding restricted stock units that will be settled in cash	1,000,000
Fair value of settled restricted stock	20,000,000	15,000,000
Unrecognized compensation costs related to nonvested restricted stock units	70,000,000
Weighted average period		2.52
Performance Share Awards [Abstract]
Performance shares settled at fair value of	18,000,000	21,000,000
Performance shares settled at fair value and paid with cash	3,000,000	10,000,000
Unrecognized compensation costs related to nonvested performance shares	$ 41,000,000
Weighted average period	2.75

[1] BGE's stock-based compensation expense (pre-tax) for the three months ended March 31, 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 three months ended March 31, 2012 shown in the table titled Components of Stock-Based Compensation Expense above. BGE's stock-based compensation expense (pre-tax) for the three months ended March 31, 2011 was $2 million.

[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] Excludes 2,141,000 and 1,348,000 of stock options issued to retirement-eligible employees as of March 31, 2012 and December 31, 2011, respectively, as they are fully vested.

[4] Includes 8,684,709 of converted Constellation options that were vested prior to the Merger on March 12, 2012.

[5] Includes 1,013,000 of stock options issued to retirement-eligible employees in 2012 that vested immediately upon the employee reaching retirement eligibility.

[6] Includes stock options issued to retirement eligible employees.

[7] Excludes 610,398 and 448,827 of restricted stock units issued to retirement-eligible employees as of March 31, 2012 and December 31, 2011, respectively, as they are fully vested

[8] Excludes 274,813 and 455,418 of performance share awards issued to retirement-eligible employees as of March 31, 2012 and December 31, 2011, respectively, as they are fully vested.

[9] Represents restricted stock units that vested but were not distributed to retirement-eligible employees during 2012.

[10] Represents performance share awards that vested but were not distributed to retirement-eligible employees during 2012.