Investments and Acquisitions (Unconsolidated Equity Investments) (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Schedule of Investments [Line Items]
Equity (income) loss from unconsolidated investments, net	$ (12.7)	$ (10.5)	$ (23.6)	$ (31.8)
ATC Holdings [Member]
Schedule of Investments [Line Items]
Equity (income) loss from unconsolidated investments, net	(10.0)	(7.8)	(19.5)	(16.5)
Non-utility wind farm In Oklahoma [Member]
Schedule of Investments [Line Items]
Equity (income) loss from unconsolidated investments, net	(1.3)	(2.5)	(2.4)	(14.6)
Other [Member]
Schedule of Investments [Line Items]
Equity (income) loss from unconsolidated investments, net	$ (1.4)	$ (0.2)	$ (1.7)	$ (0.7)