Investments (Details 2) (USD $)	2 Months Ended	12 Months Ended
	Dec. 31, 2009	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Equity in earnings of investments accounted for under the equity method of accounting
Amortization of basis difference in CENG		$ (153,100,000)	$ (195,200,000)	$ (29,600,000)
Equity investment earnings		19,800,000	25,000,000	(6,100,000)
CENG
Equity in earnings of investments accounted for under the equity method of accounting
CENG - equity investment earnings before adjustments for amortization of basis difference		148,800,000	218,800,000	33,900,000
Amortization of basis difference in CENG		(153,100,000)	(195,200,000)	(29,600,000)
Equity investment earnings	4,300,000	(4,300,000)	23,600,000	4,300,000
CENG | EDF
Equity in earnings of investments accounted for under the equity method of accounting
Expense of share-based awards		1,100,000	2,000,000	400,000
UNE
Equity in earnings of investments accounted for under the equity method of accounting
Equity investment earnings			(16,800,000)	(24,700,000)
Shipping JV
Equity in earnings of investments accounted for under the equity method of accounting
Equity investment earnings				(1,800,000)
CEP
Equity in earnings of investments accounted for under the equity method of accounting
Equity investment earnings				(4,600,000)
Qualifying facilities and domestic
Equity in earnings of investments accounted for under the equity method of accounting
Equity investment earnings		$ 24,100,000	$ 18,200,000	$ 20,700,000