Capitalization (Details 2) (USD $) In Millions, except Share data, unless otherwise specified											12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009	Dec. 31, 2008	Dec. 31, 2011 Common Stock	Dec. 31, 2010 Common Stock	Dec. 31, 2009 Common Stock	Dec. 31, 2008 Common Stock	Dec. 31, 2011 Baltimore Gas and Electric Company	Dec. 31, 2010 Baltimore Gas and Electric Company	Dec. 31, 2011 Baltimore Gas and Electric Company 7.125%, 1993 Series Cumulative preference stock not subject to mandatory redemption	Dec. 31, 2010 Baltimore Gas and Electric Company 7.125%, 1993 Series Cumulative preference stock not subject to mandatory redemption	Dec. 31, 2011 Baltimore Gas and Electric Company 6.97%, 1993 Series preference stock	Dec. 31, 2010 Baltimore Gas and Electric Company 6.97%, 1993 Series preference stock	Dec. 31, 2011 Baltimore Gas and Electric Company 6.70%, 1993 Series preference stock	Dec. 31, 2010 Baltimore Gas and Electric Company 6.70%, 1993 Series preference stock	Dec. 31, 2011 Baltimore Gas and Electric Company 6.99%, 1995 Series preference stock	Dec. 31, 2010 Baltimore Gas and Electric Company 6.99%, 1995 Series preference stock
Capitalization disclosures
Noncontrolling interests	$ 116.9	$ 88.8
BGE Preference Stock
Preferred stock, authorized shares (in shares)											6,500,000	6,500,000
Preferred stock dividend rate (as a percent)											7.125%	7.125%	6.97%	6.97%	6.70%	6.70%	6.99%	6.99%
Preferred stock, outstanding shares (in shares)											400,000	400,000	500,000	500,000	400,000	400,000	600,000	600,000
BGE preference stock	190.0	190.0							190.0	190.0	40.0	40.0	50.0	50.0	40.0	40.0	60.0	60.0
Preferred stock, callable amount (in dollars per share)												$ 100.71		$ 100.70		$ 100.67		$ 101.40
Common shareholders' equity:
Common shareholders' equity	7,093.9	7,829.2							1,293.1	1,293.1
Common stock, authorized shares (in shares)	600,000,000	600,000,000
Common stock, issued shares (in shares)	201,686,291	199,788,658
Common stock, outstanding shares (in shares)	201,686,291	199,788,658			201,686,000	199,789,000	200,985,000	199,129,000
Common stock reserved for the long-term incentive plans (in shares)	10,143,863
Common stock reserved for the shareholder investment plan (in shares)	8,542,059
Common stock reserved for the employee savings plan (in shares)	1,223,050
Retained earnings	4,738.0	5,270.8							817.0	779.5
Total common shareholders' equity	7,093.9	7,829.2							2,110.7	2,073.2
Accumulated other comprehensive (loss) income:
Hedging instruments	(404.0)	(228.7)
Available-for-sale securities	38.9	34.5
Defined benefit plans	(558.3)	(481.1)
Foreign currency translation and other	(12.9)	2.0
Total accumulated other comprehensive loss	(936.3)	(673.3)							0.6	0.6
Total equity	7,400.8	8,108.0	8,962.4	3,391.5	3,292.2	3,231.7	3,229.6	3,164.5
Total Capitalization	$ 12,245.6	$ 12,556.8