Common Stock (Details) (USD $)	12 Months Ended
	Dec. 31, 2012		Dec. 31, 2011		Dec. 31, 2010		Jun. 30, 2012	Jan. 31, 2011
Common Stock [Abstract]
Common Stock without par - Authorized	2,000,000,000		2,000,000,000
Common Stock without par - Outstanding	854,781,389		663,368,958					855,019,272
Common Stock par - Authorized			250,000,000
Common Stock reserved for warrants	24,727
Authorized Shares for LTIP [Abstract]
Authorized Shares for LTIP	20,000,000
Share Based Compensation Components [Abstract]
Performance shares	$ 46,000,000		$ 26,000,000		$ 6,000,000
Stock options	15,000,000		8,000,000		10,000,000
Restricted stock units	50,000,000		31,000,000		21,000,000
Other stock-based awards	4,000,000		4,000,000		4,000,000
Total stock-based compensation included in operating and maintenance expense	115,000,000		69,000,000		41,000,000
Income Tax Benefit	(44,000,000)		(27,000,000)		(16,000,000)
Total after-tax stock based compensation expense	71,000,000		42,000,000		25,000,000
Share Based Compensation Pre Tax Expense [Line Items]
Pre-tax stock based compensation expense	115,000,000	[1]	69,000,000		41,000,000
Realized tax benefit when exercised/distributed:
Stock options	3,000,000		2,000,000		5,000,000
Restricted stock units	11,000,000		8,000,000		9,000,000
Performance share awards	7,000,000		7,000,000		13,000,000
Stock deferral plan	0		1,000,000		1,000,000
Excess tax benefits included in other financing activities of Exelon's Consolidated Statements of Cash Flows:
Stock options	2,000,000		1,000,000		3,000,000
Restricted stock units	0		0		0
Performance share awards	0		0		0
Stock deferral plan	0		0		0
Share Based Compensation Arrangement By Share Based Payment Award Options Outstanding Roll Forward
Exercised - shares	(1,776,041)
Exercisable stock options - aggregate intrinsic value	13,000,000
Share Based Compensation Arrangement By Share Based Payment Award Equity Instruments Other Than Options Nonvested Roll Forward
Stock Based Compensation Other Than Options Converted Acquiree	11,194,151
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			448,827
Stock based compensation issued to retirement eligible employees that vested immediately on the date of the grant.			1,348,000
Fair value of each option estimated using the Black-Scholes-Merton option-pricing model
Dividend yield	0.0528%		0.0484%		0.0456%
Expected volatility	0.232%		0.244%		0.271%
Risk-free interest rate	0.013%		0.0265%		0.0296%
Expected life (years)	6 years 3 months 1 day		6 years 3 months 1 day		6 years 3 months 1 day
Weighted average grant date fair value	$ 4.18		$ 6.22		$ 8.08
Additional Information Regarding Stock Options Exercised [Abstract]
Intrinsic value	19,000,000	[2]	5,000,000	[2]	13,000,000	[2]
Cash received for exercise price	47,000,000		13,000,000		24,000,000
Unrecognized compensation costs related to nonvested stock options	6,000,000
Weighted Average Period Non Vested Stock Options Are Expected To Be Recognized Over	2 years 5 months
Restricted Stock Units [Abstract]
Weighted average grant date fair value	39.94		43.33		44.23
Obligations related to outstanding restricted stock units not yet settled			46,000,000				58,000,000
Obligations related to outstanding restricted stock units that will be settled in cash	43,000,000
Fair value of settled restricted stock	25,000,000		19,000,000		22,000,000
Performance Share Awards [Abstract]
Weighted average grant date fair value	39.71		43.52		60.82
Performance shares settled at fair value of	23,000,000		22,000,000		32,000,000
Performance shares settled at fair value and paid with cash	3,000,000		10,000,000		20,000,000
Unrecognized compensation costs related to nonvested performance shares	9,000,000
Weighted average period	1 year 11 months
Obligation Related To Outstanding Performance Share Awards [Abstract]
Current Liabilities	7,000,000	[3]	3,000,000	[3]
Deferred credits and other liabilities	11,000,000	[4]	0	[4]
Common stock	35,000,000		30,000,000
Total	53,000,000		33,000,000
Share Repurchases [Abstract]
Number of shares of common stock purchased under 2004 share repurchase program	35,000,000
Value of shares of common stock purchased under 2004 share repurchase program	2,300,000,000
Approved number of shares of common stock for repurchased under Q3 2008 share repurchase program	1,500,000,000
Stock Options [Member]
Share Based Compensation Arrangement By Share Based Payment Award Options Outstanding Roll Forward
Shares outstanding, beginning balance - shares	11,553,761
Granted - shares	2,372,000
Converted Options Acquiree	11,194,151
Forfeited - shares	(980,986)
Expired - shares	(459,104)
Shares outstanding, ending balance - shares	21,903,781
Exercisable stock options - shares	19,943,116	[5]
Shares outstanding, beginning balance - weighted average exercise price (per share)	$ 48.49
Grants - weighted average exercise price (per share)	$ 39.66
Converted options of acquiree	$ 41.35
Exercised - weighted average exercise price (per share)	$ 26.41
Forfeited - weighted average exercise price (per share)	$ 42.90
Expired - weighted average exercise price (per share)	$ 49.45
Shares outstanding, ending balance - weighted average exercise price (per share)	$ 45.91
Exercisable stock options - weighted average exercise price (per share)	$ 46.40	[5]
Shares outstanding, ending balance - weighted average remaining contractual life (years)	5 years 7 months 2 days
Exercisable stock options - weighted average remaining contractual life (years)	5 years 3 months 1 day
Shares outstanding, ending balance - aggregate intrinsic value	13,000,000
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	1,699,000
Stock based compensation issued to retirement eligible employees that vested immediately on the date of the grant.	2,647,536
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
Stock Based Compensation Converted Acquirer Shares	11,194,151
Value of stock based compensation converted	65,000,000
No Sale Restricted Stock of Acquiree converted	165,219,000,000
Nonvested Stock Option [Member]
Share Based Compensation Arrangement By Share Based Payment Award Options Outstanding Roll Forward
Shares outstanding, beginning balance - shares	877,050	[6]
Granted - shares	2,372,000	[7]
Vested - shares	(12,023,432)	[7]
Forfeited - shares	(459,104)
Shares outstanding, ending balance - shares	1,960,665	[6]
Shares outstanding, beginning balance - weighted average exercise price (per share)	$ 48.66	[6]
Grants - weighted average exercise price (per share)	$ 39.66	[7]
Vested - weighted average exercise price (per share)	$ 41.37	[7]
Forfeited - weighted average exercise price (per share)	$ 49.45
Shares outstanding, ending balance - weighted average exercise price (per share)	$ 40.56	[6]
Restricted Stock [Member]
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]
Granted - shares	1,332,214
Stock Based Compensation Other Than Options Converted Acquiree	825,735
Vested - shares	(479,805)
Forfeited - shares	(76,484)
Undistributed Vested Awards - shares	(646,983)	[9]
Equity instruments other than options - shares, ending balance	2,029,161	[8]
Equity instruments other than options - Weighted average grant date fair value (per share), beginning balance	$ 48.08	[8]
Granted - Weighted average grant date fair value (per share)	$ 39.94
Vested - Weighted average grant date fair value (per share)	$ 46.36
Forfeited - Weighted average grant date fair value (per share)	$ 42.21
Undistributed Vested Awards - weighted average exercise price (per share)	$ 40.75	[9]
Equity instruments other than options - Weighted average grant date fair value (per share), ending balance	$ 42.12	[8]
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	686,121
Share Based Compensation Acquisition Arrangement [Abstract]
No Sale Restricted Stock Converted Shares	153,654
No Sale Restricted Stock Converted Value	6,000,000
Performance Share Awards [Member]
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	346,848	[10]
Granted - shares	1,429,189
Vested - shares	(167,048)
Forfeited - shares	(116,388)
Undistributed Vested Awards - shares	(179,867)	[11]
Equity instruments other than options - shares, ending balance	1,312,734	[10]
Equity instruments other than options - Weighted average grant date fair value (per share), beginning balance	$ 45.37	[10]
Granted - Weighted average grant date fair value (per share)	$ 39.72
Vested - Weighted average grant date fair value (per share)	$ 47.46
Forfeited - Weighted average grant date fair value (per share)	$ 39.78
Undistributed Vested Awards - weighted average exercise price (per share)	$ 40.72	[11]
Equity instruments other than options - Weighted average grant date fair value (per share), ending balance	$ 40.08	[10]
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	204,643		455,418
Exelon Generation Co L L C [Member]
Share Based Compensation Pre Tax Expense [Line Items]
Pre-tax stock based compensation expense	42,000,000	[1]	31,000,000		21,000,000
Commonwealth Edison Co [Member]
Common Stock [Abstract]
Par value of common stock	$ 12.50		$ 12.50
Common Stock par - Authorized	250,000,000
Common Stock par - Outstanding	127,016,761		127,016,529					127,016,761
Warrants Outstanding	74,182		75,096
Common Stock reserved for warrants			25,032
Share Based Compensation Pre Tax Expense [Line Items]
Pre-tax stock based compensation expense	11,000,000	[1]	5,000,000		3,000,000
PECO Energy Co [Member]
Common Stock [Abstract]
Common Stock without par - Authorized	500,000,000		500,000,000
Common Stock without par - Outstanding	170,478,507		170,478,507					170,478,507
Share Based Compensation Pre Tax Expense [Line Items]
Pre-tax stock based compensation expense	5,000,000	[1]	5,000,000		3,000,000
Baltimore Gas and Electric Company [Member]
Common Stock [Abstract]
Common Stock without par - Authorized	175,000,000		175,000,000
Common Stock without par - Outstanding	1,000		1,000
Share Based Compensation Pre Tax Expense [Line Items]
Pre-tax stock based compensation expense			6,000,000		4,000,000
Business Services Company [Member]
Share Based Compensation Pre Tax Expense [Line Items]
Pre-tax stock based compensation expense	$ 52,000,000	[1],[12]	$ 28,000,000	[12]	$ 14,000,000	[12]

[1] For BGE, reflects BGE's stock-based compensation expense for the year ended December 31, 2012. For Exelon and Generation, includes the stock-based compensation expense of Constellation and BGE from the date of the merger, March 12, 2012, through December 31, 2012.

[2] The difference between the market value on the date of exercise and the option exercise price.

[3] Represents the current liability related to performance share awards expected to be settled in cash.

[4] Represents the long-term liability related to performance share awards expected to be settled in cash.

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

[6] Excludes 2,647,536 and 1,348,000 of stock options issued to retirement-eligible employees as of December 31, 2012 and December 31, 2011, respectively, as they are fully vested.

[7] Includes 1,699,000 of stock options issued to retirement-eligible employees in 2012 that vested immediately upon the employee reaching retirement eligibility.

[8] Excludes 686,121 and 448,827 of restricted stock units issued to retirement-eligible employees as of December 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] Excludes 204,643 and 455,418 of performance share awards issued to retirement-eligible employees as of December 31, 2012 and December 31, 2011, respectively, as they are fully vested.

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

[12] (a)         For BGE, reflects BGE's stock-based compensation expense for the year ended December 31, 2012. For Exelon and Generation, includes the stock-based compensation expense of Constellation and BGE from the date of the merger, March 12, 2012, through December 31, 2012. (b)        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.