Equity Method Investments (Narrative) (Details) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2018 USD ($)	Sep. 30, 2017 USD ($)	Sep. 30, 2018 USD ($)	Sep. 30, 2017 USD ($)
Schedule of Equity Method Investments [Line Items]
Loss from equity method investments	$ 12.6	$ 22.4	$ 58.6	$ 77.2
Equity method investments summarized financial data basis			100.00%
Equity Method Investment, Other than Temporary Impairment	39.0
Reduction in Equity Method Investment Long-Term Obligation	40.0		$ 40.0
Equity Method Investment, Realized Gain (Loss) on Disposal	$ 1.0
Clean energy investments
Schedule of Equity Method Investments [Line Items]
Number of equity method investments	3		3