Regulatory Assets (net) (Details) (Baltimore Gas and Electric Company, USD $) In Millions, unless otherwise specified				10 Months Ended
	Dec. 31, 2010 Deferral of electric deferred income tax relating to 2010 elimination of the tax exempt status of drug subsidies under Medicare Part D	Dec. 31, 2010 Workforce reduction costs	Feb. 28, 2010 Storm costs	Sep. 30, 2011 year	Mar. 31, 2011
Regulatory assets and liabilities
Total amount added to regulatory assets (net) per Maryland PSC distribution rate order	$ 2.7	$ 0.4	$ 15.8		$ 18.9
Term of recovery from customers (in years)				5