SCHEDULE II - VALUATION AND QUALIFYING ACCOUNTS (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Baltimore Gas and Electric Company | Accumulated Provision for Uncollectibles
Changes in valuation and qualifying accounts:
Balance at beginning of period	$ 35.9	$ 47.2	$ 34.2
Additions Charged to costs and expenses	39.4	45.6	41.8
(Deductions) - Describe	(37.6)	(56.9)	(28.8)
Balance at end of period	37.7	35.9	47.2
Constellation Energy; | Accumulated Provision for Uncollectibles
Changes in valuation and qualifying accounts:
Balance at beginning of period	172.9	160.6	240.6
Additions Charged to costs and expenses	84.5	76.2	71.2
Additions Charged to Other Accounts - Describe	(6.3)	27.6	(5.0)
(Deductions) - Describe	(48.5)	(91.5)	(146.2)
Balance at end of period	202.6	172.9	160.6
Constellation Energy; | Valuation Allowance Net unrealized (gain) loss on available for sale securities
Changes in valuation and qualifying accounts:
Balance at beginning of period	(2.9)	(2.8)	2.1
Additions Charged to costs and expenses			(3.6)
Additions Charged to Other Accounts - Describe	0.1	(0.1)	(1.3)
Balance at end of period	(2.8)	(2.9)	(2.8)
Constellation Energy; | Valuation allowance Net unrealized (gain) loss on nuclear decommissioning trust funds
Changes in valuation and qualifying accounts:
Balance at beginning of period			(49.6)
Additions Charged to Other Accounts - Describe			(201.0)
(Deductions) - Describe			$ 250.6