Investments (Narrative) (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Schedule of Investments [Line Items]
Equity (income) loss from unconsolidated investments, net	$ (10.5)	$ (11.3)	$ (31.8)	$ (22.8)
Non-utility wind farm In Oklahoma [Member]
Schedule of Investments [Line Items]
Equity (income) loss from unconsolidated investments, net	$ (2.5)	$ 0.0	$ (14.6)	$ 0.0