Equity Method Investments (Narrative) (Details) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2018 USD ($)	Jun. 30, 2017 USD ($)	Jun. 30, 2018 USD ($)	Jun. 30, 2017 USD ($)
Schedule of Equity Method Investments [Line Items]
Loss from equity method investments	$ 22.9	$ 21.7	$ 46.0	$ 54.9
Equity method investments summarized financial data basis			100.00%
Clean energy investments
Schedule of Equity Method Investments [Line Items]
Number of equity method investments	5		5