Investments (Unconsolidated Equity Investments) (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014
Schedule of Investments [Line Items]
Equity (income) loss from unconsolidated investments, net	$ (11.3)	$ (11.3)	$ (17.8)	$ (22.7)
WPL [Member]
Schedule of Investments [Line Items]
Equity (income) loss from unconsolidated investments, net	(11.3)	(11.4)	(19.1)	(22.8)
ATC [Member]
Schedule of Investments [Line Items]
Equity (income) loss from unconsolidated investments, net	(10.9)	(11.1)	(18.7)	(22.3)
ATC [Member] | WPL [Member]
Schedule of Investments [Line Items]
Equity (income) loss from unconsolidated investments, net	(10.9)	(11.1)	(18.7)	(22.3)
Other [Member]
Schedule of Investments [Line Items]
Equity (income) loss from unconsolidated investments, net	(0.4)	(0.2)	0.9	(0.4)
Other [Member] | WPL [Member]
Schedule of Investments [Line Items]
Equity (income) loss from unconsolidated investments, net	$ (0.4)	$ (0.3)	$ (0.4)	$ (0.5)