Commitments, Guarantees, and Contingencies (Details 3) (USD $)	12 Months Ended				1 Months Ended	2 Months Ended	1 Months Ended	3 Months Ended	12 Months Ended			12 Months Ended		1 Months Ended		3 Months Ended	12 Months Ended		12 Months Ended
	Dec. 31, 2011	Nov. 06, 2011	Dec. 31, 2009	Nov. 06, 2009 CENG	Aug. 31, 2011 Litigation, merger with Exelon Lawsuit	May 31, 2011 Litigation, merger with Exelon company Lawsuit	Aug. 31, 2011 Litigation, Securities Class Action complaint	Nov. 30, 2008 Litigation, Securities Class Action Lawsuit	Dec. 31, 2008 Litigation, Securities Class Action Lawsuit	Dec. 31, 2011 Litigation, Asbestos Claimant	Dec. 31, 2011 Litigation, FERC	Dec. 31, 1999 Environmental Matters, Solid and Hazardous Waste Defendant	Dec. 31, 2011 Environmental Matters, Solid and Hazardous Waste	Jan. 31, 2009 Environmental Matters, Air Quality	Oct. 31, 2007 Environmental Matters, Water Quality	Dec. 31, 2011 Environmental Matters, Water Quality	Dec. 31, 2011 Environmental Matters, Water Quality	Feb. 29, 2012 Property and Accidental Outage Insurance	Dec. 31, 2011 Nuclear Accidents CENG Unit
Loss Contingencies
Number of merged companies						2
Number of lawsuits filed						12
Number of lawsuits for which motions are filed for consolidation						3
Number of lawsuits filed for breach of fiduciary duties					2
Number of lawsuits filed in District Court								3
Number of lawsuits transferred to other District Court for coordination									2
Number of complaints filed							3
Number of defendants in addition to BGE and Constellation Energy												19
Number of claimants										483
Approximate ownership percentage in Keystone plant (as a percent)														20.99%
Minimum estimated clean-up costs for all potentially responsible parties													$ 50,000,000
Maximum estimated clean-up costs for all potentially responsible parties													64,000,000
Consent decree penalty															1,000,000
Estimate of possible loss											100,000,000							94,600,000
Accrual for Environmental (Loss) Contingencies
Environmental loss contingencies															22,700,000	17,000,000	17,000,000
Net Increase (Decrease) to Environmental loss contingencies																12,100,000
Environmental loss contingencies payments																	5,700,000
Percent of membership interest in CENG sold		49.99%	49.99%	49.99%
Percentage of ownership interest in CENG			50.01%	50.01%
Number of nuclear generating units owned, operated and maintained by CENG																			3
Commercial insurance available																			375,000,000
Retrospective premium assessment per reactor, per incident																			117,500,000
Total insurance available for public liability related to nuclear accidents																			12,600,000,000
Limit on assessment of retrospective premiums per incident																			587,500,000
Maximum amount of retrospective premium payable per nuclear incident per year																			87,500,000
Maximum per occurrence insurance coverage for Certified acts of terrorism	1,000,000,000
Maximum annual aggregate insurance coverage for non-certified acts of terrorism	$ 1,000,000,000