Commitments and Contingencies, Long-Term Power Sales Contracts, Litigation (Details 2) (USD $) In Millions, unless otherwise specified	2 Months Ended	3 Months Ended	12 Months Ended	6 Months Ended		12 Months Ended		1 Months Ended		6 Months Ended
	May 31, 2011 Litigation, merger with Exelon	Nov. 30, 2008 Litigation, Securities Class Action	Dec. 31, 2008 Litigation, Securities Class Action	Jun. 30, 2011 Litigation, Mercury	Jun. 30, 2011 Litigation, Asbestos	Dec. 31, 1999 Environmental Matters, Solid and Hazardous Waste	Jun. 30, 2011 Environmental Matters, Solid and Hazardous Waste	Jan. 31, 2009 Environmental Matters, Air Quality	Oct. 31, 2007 Environmental Matters, Water Quality	Jun. 30, 2011 Environmental Matters, Water Quality
Loss Contingencies
Lawsuits filed, number	12			70
Number of lawsuits for which motions are filed for consolidation	3
Lawsuits filed in District Court, number		3
Lawsuits transferred to other District Court for coordination, number			2
Defendants in addition to BGE and Constellation Energy, number				11		19
Claimants, number				132	477
Compensatory damages sought per claimant				$ 20
Approximate ownership percentage in Keystone plant (as a percent)								20.99%
Minimum estimated clean-up costs for all potentially responsible parties							50
Maximum estimated clean-up costs for all potentially responsible parties							64
Consent decree penalty									1.0
Accrual for Environmental (Loss) Contingencies
Environmental loss contingencies									10.6	3.4
Environmental loss contingencies payments										7.2
Additional costs reasonably possible										$ 10