Other Events (Details 3) (USD $)	1 Months Ended				3 Months Ended				12 Months Ended
	Apr. 30, 2011	Dec. 31, 2009 Agency	Nov. 30, 2009	Dec. 31, 2008	Dec. 31, 2011	Dec. 31, 2010	Sep. 30, 2010	Dec. 31, 2009 Agency	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009 Agency	Nov. 06, 2011	Nov. 06, 2009
Pending merger with Exelon Corporation
Net (loss) gain on divestitures, pre-tax									$ 57,300,000	$ 245,800,000	$ (468,800,000)
Impairment losses and other costs									891,000,000	2,476,800,000	124,700,000
Number of common shares of Constellation Energy to be cancelled and converted into the right to receive for each share of Exelon (in shares)	0.93
Gain on Sale of 49.99% Membership Interest in CENG to EDF
Percent of membership interest in CENG sold		49.99%						49.99%			49.99%	49.99%
Purchase price of 49.99% membership interest in CENG sold to EDF				4,500,000,000
Approximate amount used to estimate the one-time per customer distribution rate credit liability (in dollars per customer)								100
Equity contribution to BGE to fund the after-tax amount of the rate credit		66,000,000
Cash capital contribution commitment to BGE		250,000,000
Equity ratio below which BGE will not pay common dividends to its holding company (as a percent)											48.00%
Number of major credit rating agencies to have assigned below investment grade rating for senior unsecured credit		2						2			2
Aggregate number of major credit rating agencies		3						3			3
Cap for rate increase in first electric distribution rate case (as a percent)											5.00%
Maximum rate of cost allocation to BGE (as a percent)											31.00%
Proceeds from sale of 49.99% membership interest in CENG			3,500,000,000								3,528,700,000
Redemption of Series B Preferred Stock held by EDF													1,000,000,000
Percentage of ownership interest in equity investment		50.01%						50.01%			50.01%
Carrying amount of CENG's assets and liabilities prior to deconsolidation		2,400,000,000						2,400,000,000			2,400,000,000
Basis difference in investment in CENG		3,900,000,000			453,100,000		1,500,000,000	3,900,000,000	453,100,000		3,900,000,000
Pre-tax gain on sale recognized
Fair value of the consideration received from EDF			4,700,000,000
Estimated fair value of our retained interest in CENG		5,100,000,000						5,100,000,000			5,100,000,000
Carrying amount of CENG's assets and liabilities prior to deconsolidation		(2,400,000,000)						(2,400,000,000)			(2,400,000,000)
Pre-tax gain on sale of interest in CENG											7,445,600,000
Carrying value of equity method investment					2,272,800,000	3,174,200,000			2,272,800,000	3,174,200,000
Impairment charges on equity method investment					891,000,000	8,400,000	2,468,400,000
Gain on sale of working interests in another natural gas property in Texas region									600,000
CENG
Pending merger with Exelon Corporation
Share in gain on U.S. department of energy settlements									50.01%
Gain on Sale of 49.99% Membership Interest in CENG to EDF
Percent of membership interest in CENG sold													49.99%
Percentage of ownership interest in equity investment					50.01%				50.01%				50.01%
Calvert Cliffs nuclear power plant
Pending merger with Exelon Corporation
Proceeds from U.S. Department of Energy settlement									39,400,000
Ginna nuclear power plant
Pending merger with Exelon Corporation
Proceeds from U.S. Department of Energy settlement									54,400,000
Subsidiary owning natural gas assets in south Texas
Pending merger with Exelon Corporation
Proceeds from sale of interest in subsidiary									93,000,000
Subsidiary owning natural gas assets in south Texas | NewEnergy
Pending merger with Exelon Corporation
Net (loss) gain on divestitures, pre-tax									23,000,000
Qualifying facilities and domestic
Pending merger with Exelon Corporation
Impairment losses and other costs					$ 66,800,000				$ 66,800,000
Constellation Energy.
Pending merger with Exelon Corporation
Number of common shares of Constellation Energy to be cancelled and converted into the right to receive for each share of Exelon (in shares)	0.93