Equity Method Investments (Narrative) (Details) $ in Millions	3 Months Ended
	Mar. 31, 2018 USD ($)	Mar. 31, 2017 USD ($)
Schedule of Equity Method Investments [Line Items]
Loss from equity method investments	$ 23.1	$ 33.2
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