Regulatory Assets (net) (Details) (USD $) In Millions, unless otherwise specified					7 Months Ended	9 Months Ended	12 Months Ended												12 Months Ended			1 Months Ended			12 Months Ended			12 Months Ended	60 Months Ended				12 Months Ended	1 Months Ended			1 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2011 Baltimore Gas and Electric Company	Dec. 31, 2010 Baltimore Gas and Electric Company	Dec. 31, 2007 Deferred Fuel Costs - Rate stabilization deferral Baltimore Gas and Electric Company Y	Dec. 31, 2009 Deferred Fuel Costs - Rate stabilization deferral Baltimore Gas and Electric Company M	Dec. 31, 2011 Deferred Fuel Costs - Rate stabilization deferral Baltimore Gas and Electric Company	Dec. 31, 2010 Deferred Fuel Costs - Rate stabilization deferral Baltimore Gas and Electric Company	Dec. 31, 2007 Deferred Fuel Costs - Rate stabilization deferral Baltimore Gas and Electric Company	May 31, 2007 Deferred Fuel Costs - Rate stabilization deferral Baltimore Gas and Electric Company	Dec. 31, 2011 Deferred Fuel Costs - Other Baltimore Gas and Electric Company	Dec. 31, 2010 Deferred Fuel Costs - Other Baltimore Gas and Electric Company	Dec. 31, 2011 Electric generation-related regulatory asset Baltimore Gas and Electric Company	Dec. 31, 2010 Electric generation-related regulatory asset Baltimore Gas and Electric Company	Dec. 31, 2011 Net cost of removal Baltimore Gas and Electric Company	Dec. 31, 2010 Net cost of removal Baltimore Gas and Electric Company	Dec. 31, 2011 Income taxes recoverable through future rates (net) Baltimore Gas and Electric Company	Dec. 31, 2010 Income taxes recoverable through future rates (net) Baltimore Gas and Electric Company	Dec. 31, 2010 Deferred BGE Smart Energy Savers Program Baltimore Gas and Electric Company	Dec. 31, 2008 Deferred BGE Smart Energy Savers Program Baltimore Gas and Electric Company	Dec. 31, 2011 Deferred BGE Smart Energy Savers Program Baltimore Gas and Electric Company	Aug. 31, 2010 Deferred Advanced Meter Infrastructure Costs Baltimore Gas and Electric Company module	Dec. 31, 2011 Deferred Advanced Meter Infrastructure Costs Baltimore Gas and Electric Company	Dec. 31, 2010 Deferred Advanced Meter Infrastructure Costs Baltimore Gas and Electric Company	Dec. 31, 1998 Deferred postretirement and postemployment benefit costs Baltimore Gas and Electric Company	Dec. 31, 2011 Deferred postretirement and postemployment benefit costs Baltimore Gas and Electric Company	Dec. 31, 2010 Deferred postretirement and postemployment benefit costs Baltimore Gas and Electric Company	Dec. 31, 2010 Deferred environmental costs Baltimore Gas and Electric Company Y	Nov. 30, 2010 Deferred environmental costs Baltimore Gas and Electric Company	Dec. 31, 2011 Deferred environmental costs Baltimore Gas and Electric Company	Dec. 31, 2011 Workforce reduction costs Baltimore Gas and Electric Company	Dec. 31, 2010 Workforce reduction costs Baltimore Gas and Electric Company	Dec. 31, 2009 2008 Workforce reduction program Baltimore Gas and Electric Company	May 31, 2011 2010 Workforce reduction program Baltimore Gas and Electric Company	Dec. 31, 2011 Other (net) Baltimore Gas and Electric Company	Dec. 31, 2010 Other (net) Baltimore Gas and Electric Company	Dec. 31, 2010 Deferred storm costs Baltimore Gas and Electric Company Y	Dec. 31, 2011 Deferred storm costs Baltimore Gas and Electric Company
Regulatory assets and liabilities
Total regulatory assets (net)			$ 495.6	$ 452.8			$ 358.3	$ 415.6			$ 61.0	$ 8.8	$ 71.4	$ 86.9	$ (218.2)	$ (210.5)	$ 71.4	$ 68.3	$ 64.3		$ 123.5		$ 15.4	$ 12.2		$ 5.2	$ 6.4	$ 5.6		$ 3.1	$ 1.1	$ 1.3			$ (9.0)	$ (6.1)		$ 12.4
Less: Current portion of regulatory assets (net)	153.7	78.7	153.7	78.7
Long-term portion of regulatory assets (net)	341.9	374.1	341.9	374.1
Rate cap for BGE residential electric customers from July 1, 2006 until May 31, 2007 (as a percent)										15.00%
Deferred expense related to electricity purchased for resale									306.4
Recovered portion of regulatory assets							57.2	61.8
Maximum term of amortizing the rate stabilization deferral into earnings (in years)					10
Term of recovery from customers (in months)						21
Portion of electric generation-related regulatory asset representing income taxes recoverable that do not earn a regulated rate of return													56.0	53.3
Amortization period of deferred costs (in years)																			5Y	5Y					15Y								5Y	5Y
Residential and commercial electric and gas smart meters and modules																						2,000,000
Total cost of smart grid pilot program																						11.3
Amortization of deferred environmental costs incurred through October 1995																												21.6
Amount of deferred environmental costs incurred from November 1995 through June 2000 being amortized																												6.4
Amortization term for deferred environmental costs incurred through June 2000 (in years)																												10
Rate relief for clean-up costs and received																												5.4	1.0
Amortization term for deferred environmental costs incurred from July 2000 through November 2005 (in years)																												10
Total amount added to regulatory assets (net) per Maryland PSC distribution rate order																																					$ 15.8
Maximum term over which the regulatory asset associated with the deferral is to be amortized (in years)																																					5