Stock-Based Compensation Plans (Details) (USD $)	3 Months Ended		9 Months Ended			9 Months Ended		3 Months Ended		9 Months Ended			9 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			3 Months Ended				9 Months Ended
	Sep. 30, 2012 Years	Sep. 30, 2011 Years	Sep. 30, 2012 Years	Sep. 30, 2011 Years	Dec. 31, 2011	Sep. 30, 2012 Stock Options [Member]		Mar. 11, 2012 Nonvested Stock Option [Member]		Sep. 30, 2012 Nonvested Stock Option [Member]		Dec. 31, 2011 Nonvested Stock Option [Member]	Sep. 30, 2012 Restricted Stock [Member]		Dec. 31, 2011 Restricted Stock [Member]	Sep. 30, 2012 Performance Share Awards [Member]		Dec. 31, 2011 Performance Share Awards [Member]	Sep. 30, 2012 Exelon Generation Co L L C [Member]	Sep. 30, 2011 Exelon Generation Co L L C [Member]	Sep. 30, 2012 Exelon Generation Co L L C [Member]	Sep. 30, 2011 Exelon Generation Co L L C [Member]	Sep. 30, 2012 Commonwealth Edison Co [Member]	Sep. 30, 2011 Commonwealth Edison Co [Member]	Sep. 30, 2012 Commonwealth Edison Co [Member]	Sep. 30, 2011 Commonwealth Edison Co [Member]	Sep. 30, 2012 PECO Energy Co [Member]	Sep. 30, 2011 PECO Energy Co [Member]	Sep. 30, 2012 PECO Energy Co [Member]	Sep. 30, 2011 PECO Energy Co [Member]	Mar. 11, 2012 Baltimore Gas and Electric Company [Member]	Sep. 30, 2012 Baltimore Gas and Electric Company [Member]		Sep. 30, 2011 Baltimore Gas and Electric Company [Member]	Sep. 30, 2012 Baltimore Gas and Electric Company [Member]		Sep. 30, 2011 Baltimore Gas and Electric Company [Member]	Sep. 30, 2012 Business Services Company [Member]		Sep. 30, 2011 Business Services Company [Member]		Sep. 30, 2012 Business Services Company [Member]		Sep. 30, 2011 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	854,283,102		854,283,102		663,000,000
Authorized Shares for LTIP [Abstract]
Authorized Shares for LTIP	20,000,000		20,000,000
Share Based Compensation Components [Abstract]
Performance shares	$ 5,000,000	$ 6,000,000	$ 32,000,000	$ 17,000,000
Stock options	2,000,000	1,000,000	13,000,000	7,000,000
Restricted stock units	12,000,000	5,000,000	41,000,000	26,000,000
Other stock-based awards	1,000,000	1,000,000	3,000,000	3,000,000
Total stock-based compensation included in operating and maintenance expense	20,000,000	13,000,000	89,000,000	53,000,000
Income Tax Benefit	(8,000,000)	(5,000,000)	(34,000,000)	(21,000,000)
Total after-tax stock based compensation expense	12,000,000	8,000,000	55,000,000	32,000,000
Share Based Compensation Pre Tax Expense [Line Items]
Pre-tax stock based compensation expense	20,000,000	13,000,000	89,000,000	53,000,000															9,000,000	6,000,000	33,000,000	24,000,000	2,000,000	1,000,000	9,000,000	4,000,000	1,000,000	1,000,000	4,000,000	4,000,000	2,000,000	1,000,000	[1]	1,000,000	4,000,000	[1]	5,000,000	7,000,000	[2]	5,000,000	[2]	39,000,000	[2],[3]	21,000,000	[2],[3]
Share Based Compensation Arrangement By Share Based Payment Award Options Outstanding Roll Forward
Shares outstanding, beginning balance - shares						11,553,761		877,050	[4]	877,050	[4]
Granted - shares						2,372,000				2,372,000	[5]
Converted Options Acquiree						11,194,151		8,684,709		11,194,151
Exercised - shares						1,575,275
Vested - shares										11,889,175	[5],[6]
Forfeited - shares						28,142				488,434
Expired - shares						488,434
Shares outstanding, ending balance - shares						23,028,061				2,065,592	[4]
Exercisable stock options - shares						20,962,469	[7]
Shares outstanding, beginning balance - weighted average exercise price (per share)						$ 48.49		$ 48.66	[4]	$ 48.66	[4]
Granted - weighted average exercise price (per share)						$ 39.66				$ 39.66	[5]
Converted options of acquiree						$ 41.35				$ 41.35			$ 38.91
Exercised - weighted average exercise price (per share)						$ 26.57
Vested - weighted average exercise price (per share)										$ 41.39	[5],[6]
Forfeited - weighted average exercise price (per share)						$ 44.88				$ 48.59
Expired - weighted average exercise price (per share)						$ 48.59
Shares outstanding, ending balance - weighted average exercise price (per share)						$ 45.61				$ 40.60	[4]
Exercisable stock options - weighted average exercise price (per share)						$ 46.08	[7]
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	[8]		346,848	[9]
Granted - shares													1,283,292			1,249,932
Stock Based Compensation Other Than Options Converted Acquiree													825,735
Vested - shares													427,499			159,194
Forfeited - shares													47,415			113,761
Undistributed Vested Awards - shares													602,276	[10]		128,370	[11]
Equity instruments other than options - shares, ending balance													2,106,321	[8]		1,195,455	[9]
Equity instruments other than options - Weighted average grant date fair value (per share), beginning balance													$ 48.08	[8]		$ 45.37	[9]
Granted - Weighted average grant date fair value (per share)													$ 39.93			$ 39.73
Vested - Weighted average grant date fair value (per share)													$ 47.69			$ 47.66
Forfeited - Weighted average grant date fair value (per share)													$ 42.67			$ 39.79
Undistributed Vested Awards - weighted average exercise price (per share)													$ 40.53	[10]		$ 40.98	[11]
Equity instruments other than options - Weighted average grant date fair value (per share), ending balance													$ 42.27	[8]		$ 40.17	[9]
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										2,719,671		1,348,000	656,228		448,827	204,643		455,418
Stock based compensation issued to retirement eligible employees that vested immediately on the date of the grant.										1,667,000
Share Based Compensation Acquisition Arrangement [Abstract]
Fair value of stock based compensation used of acquiree	71,000,000		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	5.28%	4.84%	5.28%	4.84%
Expected volatility	23.20%	24.40%	23.20%	24.40%
Risk-free interest rate	1.30%	2.65%	1.30%	2.65%
Expected life (years)	6.25	6.25	6.25	6.25
Additional Information Regarding Stock Options Exercised [Abstract]
Unrecognized compensation costs related to nonvested stock options	8,000,000		8,000,000
Weighted Average Period Non Vested Stock Options Are Expected To Be Recognized Over	2.5		2.5
Restricted Stock Units [Abstract]
Obligations related to outstanding restricted stock units not yet settled	58,000,000		58,000,000
Obligations related to outstanding restricted stock units that will be settled in cash	1,000,000		1,000,000
Fair value of settled restricted stock	4,000,000	1,000,000	23,000,000	19,000,000
Unrecognized compensation costs related to nonvested restricted stock units	54,000,000		54,000,000
Weighted average period	2.08		2.08
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%
Performance shares settled at fair value of			22,000,000	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	$ 19,000,000		$ 19,000,000
Weighted average period	2.3		2.3

[1] BGE's stock-based compensation expense for the nine months ended September 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 nine months ended September 30, 2012 shown in the table titled Components of Stock-Based Compensation Expense above. BGE's stock-based compensation expense for the three and nine months ended September 30, 2011 was $1 million and $5 million, respectively.

[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.

[4] Excludes 2,719,671 and 1,348,000 of stock options issued to retirement-eligible employees as of September 30, 2012 and December 31, 2011, respectively, as they are fully vested.

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

[6] Includes 1,667,000 of stock options issued to retirement-eligible employees in 2012 that vested immediately upon the employee reaching retirement eligibility.

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

[8] Excludes 656,228 and 448,827 of restricted stock units issued to retirement-eligible employees as of September 30, 2012 and December 31, 2011, respectively, as they are fully vested

[9] Excludes 204,643 and 455,418 of performance share awards issued to retirement-eligible employees as of September 30, 2012 and December 31, 2011, respectively, as they are fully vested.

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

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