Investments and Acquisitions (Unconsolidated Equity Investments) (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Schedule of Investments [Line Items]
Equity (income) loss from unconsolidated investments, net	$ (11.6)	$ (9.8)	$ (35.2)	$ (41.6)
ATC Holdings [Member]
Schedule of Investments [Line Items]
Equity (income) loss from unconsolidated investments, net	(10.5)	(8.9)	(30.0)	(25.4)
Non-utility wind farm In Oklahoma [Member]
Schedule of Investments [Line Items]
Equity (income) loss from unconsolidated investments, net	(0.4)	0.1	(2.8)	(14.5)
Other [Member]
Schedule of Investments [Line Items]
Equity (income) loss from unconsolidated investments, net	$ (0.7)	$ (1.0)	$ (2.4)	$ (1.7)