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Equity method investments in unconsolidated affiliates (Details) - USD ($) $ in Millions	1 Months Ended	12 Months Ended
	Aug. 31, 2013	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Equity method investments
Carrying value		$ 286.2	$ 306.9
Equity (deficit) in earnings (loss) of equity method investments		36.7	25.5	$ 25.8
Distributions from equity method investments		(58.5)	(76.2)	(40.9)
Deficit in earnings of equity method investments, net of distributions		$ (21.8)	(50.7)	(15.1)
Frederickson
Equity method investments
Percentage of ownership interest		50.20%
Carrying value		$ 124.7	135.0
Equity (deficit) in earnings (loss) of equity method investments		$ 2.6	2.2	2.1
Orlando
Equity method investments
Percentage of ownership interest		50.00%
Carrying value		$ 8.4	10.9
Equity (deficit) in earnings (loss) of equity method investments		$ 27.0	18.6	3.3
Koma Kulshan Associates [Member]
Equity method investments
Percentage of ownership interest		49.80%
Carrying value		$ 5.4	5.7
Equity (deficit) in earnings (loss) of equity method investments		$ 0.4	0.9	0.3
Chambers
Equity method investments
Percentage of ownership interest		40.00%
Carrying value		$ 135.7	143.3
Equity (deficit) in earnings (loss) of equity method investments		$ 6.5	7.0	9.6
Selkirk Cogen Partners LP
Equity method investments
Percentage of ownership interest		17.70%
Carrying value		$ 12.0	12.0
Equity (deficit) in earnings (loss) of equity method investments		$ 0.2	$ (3.2)	8.7
Gregory Power Partners, LP
Equity method investments
Equity (deficit) in earnings (loss) of equity method investments				1.6
Gain on sale of equity method investment	$ 30.4			30.4
Other
Equity method investments
Equity (deficit) in earnings (loss) of equity method investments				$ 0.2