Investments and Acquisitions (Unconsolidated Equity Investments) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Schedule of Investments [Line Items]
Equity (income) loss from unconsolidated investments, net	$ (10.9)	$ (21.3)
ATC Holdings [Member]
Schedule of Investments [Line Items]
Equity (income) loss from unconsolidated investments, net	(9.5)	(8.7)
Non-utility wind farm In Oklahoma [Member]
Schedule of Investments [Line Items]
Equity (income) loss from unconsolidated investments, net	(1.1)	(12.1)
Other [Member]
Schedule of Investments [Line Items]
Equity (income) loss from unconsolidated investments, net	$ (0.3)	$ (0.5)