Investments (Details) (USD $) In Millions, unless otherwise specified	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009	Dec. 31, 2011 Minimum	Dec. 31, 2010 Minimum	Dec. 31, 2011 Maximum	Dec. 31, 2010 Maximum	Dec. 31, 2011 Coal	Dec. 31, 2010 Coal	Dec. 31, 2011 Hydroelectric	Dec. 31, 2010 Hydroelectric	Dec. 31, 2011 Biomass	Dec. 31, 2010 Biomass	Dec. 31, 2011 Fuel Processing	Dec. 31, 2010 Fuel Processing	Dec. 31, 2010 Solar	Dec. 31, 2011 CENG	Dec. 31, 2010 CENG	Nov. 06, 2009 CENG
Investments:
Equity method	$ 2,272.8	$ 3,174.2
Cost method		6.8
Investment in joint ventures and affiliates	$ 2,272.8	$ 3,181.0						$ 33.4	$ 65.0	$ 43.0	$ 46.3	$ 24.6	$ 55.1	$ 21.4	$ 16.7	$ 6.8	$ 2,150.4	$ 2,991.1
Percentage of ownership interest in equity investment			50.01%	20.00%	20.00%	50.01%	50.01%										50.01%		50.01%