Capitalization (Details 3) (USD $) In Millions, unless otherwise specified			1 Months Ended	12 Months Ended					12 Months Ended			1 Months Ended	12 Months Ended		1 Months Ended
	Dec. 31, 2011	Dec. 31, 2009	Jul. 31, 2009 Amended and extended existing reserve based lending facility Y	Dec. 31, 2011 Amended and extended existing reserve based lending facility denominator numerator	Feb. 28, 2011 Interest rate contracts	Dec. 31, 2011 Constellation Energy;	Dec. 31, 2010 Constellation Energy;	Dec. 31, 2010 Constellation Energy; 7.00% Fixed-Rate Notes, due April 1, 2012	Dec. 31, 2011 Constellation Energy; 5.15% Fixed-Rate Notes, due December 1, 2020	Dec. 31, 2010 Constellation Energy; 5.15% Fixed-Rate Notes, due December 1, 2020	Dec. 31, 2011 Baltimore Gas and Electric Company	Nov. 30, 2011 Baltimore Gas and Electric Company 3.50% Notes, due November 15, 2021	Dec. 31, 2011 Baltimore Gas and Electric Company 3.50% Notes, due November 15, 2021	Dec. 31, 2011 Subsidiary of Constellation Energy	Jul. 31, 2011 Subsidiary of Constellation Energy Secured Solar Credit Lending Agreement due July 7, 2014 Y	Jul. 31, 2011 Subsidiary of Constellation Energy Sacramento Solar Project Financing Agreement due December 31, 2030 Y MW	Dec. 31, 2011 Nonregulated businesses	Dec. 31, 2010 Nonregulated businesses	Dec. 31, 2011 Nonregulated businesses Secured Solar Credit Lending Agreement due July 7, 2014	Dec. 31, 2011 Nonregulated businesses Sacramento Solar Project Financing Agreement due December 31, 2030	Dec. 31, 2011 Nonregulated businesses Denver International Airport Solar Loan Agreement due June 30, 2031	Dec. 31, 2011 Nonregulated businesses Holyoke Solar, LLC Loan Agreement due December 31, 2031
Capitalization disclosures
Issuance of debt												$ 300.0
Redemption of notes at a price equal to or greater than of principal amount (as a percent)									100.00%				100.00%
Variable rate used for early redemption									Treasury rate				Treasury rate
Basis points added to variable rate used for early redemption (as a percent)									0.30%				0.25%
Long-term debt	5,024.8					2,294.1	2,499.7	213.5	550.0	550.0	2,361.9		300.0				368.8	114.7	130.0	40.7	7.5	11.0
Interest rate (as a percent)		3.50%						7.00%	5.15%	5.15%		3.50%	3.50%
Recognized pre-tax loss on redemption of debt									5.0
Notional amount, interest rate swap fair value hedge					350
Notional amount, interest rate swap not qualify as fair value hedges					150
Notional amount of fixed rate debt effectively converted to floating rate for the term of the swaps					500
Maximum borrowing capacity	130.0					4,200.0
Solar facility (MW)																30
Term of nonrecourse variable rate note for solar facility (in years)																19
Term of asset based lending agreement (in years)			3
Maximum amount up to which amount committed under senior credit facility may be increased				500											200
Notional amount of interest rate swaps																30.6
Bridge loan																26.0
Equity bridge loan																27.9
Outstanding borrowings				83.0										130.0
Current ratio to be maintained, numerator				1
Current ratio to be maintained, denominator				1
Call notice issued on 7.00 percent fixed-rate notes due April 1, 2012 with expected repurchase date of January 2011								$ 213.5
Term of senior secured credit facility (in years)															3