The number of power purchase agreements under which the project operates.

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Amount of distribution received from equity method investee for return on investment, classified as operating activities. Excludes distribution for return of investment, classified as investing activities.

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The percentage of ownership of common stock or equity participation in the investee accounted for under the equity method of accounting.

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Amount of gain (loss) on sale or disposal of an equity method investment.

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Equity method investments in unconsolidated affiliates - impairments (Details) $ in Millions	3 Months Ended		12 Months Ended			41 Months Ended
	Dec. 31, 2017 USD ($) agreement	Jun. 30, 2017 USD ($)	Dec. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)	Dec. 31, 2017 USD ($)	Jun. 18, 2018
Equity in earnings of unconsolidated affiliates
Percentage of equity method ownership interest							100.00%
Equity in earnings of unconsolidated affiliates			$ (3.0)	$ 43.2	$ (54.8)
Equity Method Investments.			96.6	140.8
Distributions from unconsolidated affiliates			59.5	61.6	47.3
Cumulative project loss			$ (62.5)	(18.4)	(102.1)
Frederickson
Equity in earnings of unconsolidated affiliates
Percentage of equity method ownership interest			50.20%
Equity in earnings of unconsolidated affiliates			$ 9.1	6.9	(27.9)
Number of PPAs under which the project operates \| agreement	3
Equity Method Investments.	$ 108.3		$ 65.2	72.0	108.3	$ 108.3
Chambers Cogen, LP
Equity in earnings of unconsolidated affiliates
Percentage of equity method ownership interest			40.00%
Equity in earnings of unconsolidated affiliates			$ (46.0)	5.6	(42.6)
Equity Method Investments.		$ 124.0	$ 9.0	$ 64.3
Selkirk Cogen Partners, LP
Equity in earnings of unconsolidated affiliates
Equity in earnings of unconsolidated affiliates					(10.6)
Distributions from unconsolidated affiliates						0.0
Cumulative project loss						$ (2.6)
Earnings from unconsolidated affiliates \| Frederickson
Equity in earnings of unconsolidated affiliates
Equity impairment other than temporary					28.3
Earnings from unconsolidated affiliates \| Chambers Cogen, LP
Equity in earnings of unconsolidated affiliates
Percentage of equity method ownership interest			40.00%
Equity impairment other than temporary		47.1	$ 49.2		47.1
Equity Method Investments.			$ 58.2
Earnings from unconsolidated affiliates \| Selkirk Cogen Partners, LP
Equity in earnings of unconsolidated affiliates
Equity impairment other than temporary		$ 10.6			10.6
Gain on sale of equity method investment					$ 1.0