Intangible Assets (Details 2) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Intangible Assets Subject to Amortization
Gross Carrying Amount	$ 716.4	$ 621.8
Accumulated Amortization	(413.9)	(406.3)
Net Asset	302.5	215.5
Amortization expense related to intangible assets	113.2	90.6	97.8
Future amortization expense related to intangible assets
2012	103.5
2013	78.4
2014	51.2
2015	29.3
2016	15.7
Nonregulated businesses
Intangible Assets Subject to Amortization
Amortization expense related to intangible assets	87.8	64.8	74.2
Future amortization expense related to intangible assets
2012	82.8
2013	62.1
2014	40.9
2015	22.4
2016	14.0
Baltimore Gas and Electric Company
Intangible Assets Subject to Amortization
Amortization expense related to intangible assets	25.4	25.8	23.6
Future amortization expense related to intangible assets
2012	20.7
2013	16.3
2014	10.3
2015	6.9
2016	1.7
Software
Intangible Assets Subject to Amortization
Gross Carrying Amount	478.6	596.8
Accumulated Amortization	(322.7)	(397.1)
Net Asset	155.9	199.7
Software | Baltimore Gas and Electric Company
Intangible Assets Subject to Amortization
Gross Carrying Amount	140.2	250.2
Accumulated Amortization	(76.8)	(171.4)
Permits and licenses
Intangible Assets Subject to Amortization
Gross Carrying Amount	4.5	2.7
Accumulated Amortization	(1.6)	(1.0)
Net Asset	2.9	1.7
Other:
Intangible Assets Subject to Amortization
Gross Carrying Amount	233.3	22.3
Accumulated Amortization	(89.6)	(8.2)
Net Asset	$ 143.7	$ 14.1