Investments (Unconsolidated Equity Investments) (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2014	Jun. 30, 2013	Jun. 30, 2014	Jun. 30, 2013
Schedule of Equity Method Investments [Line Items]
Equity (income) loss from unconsolidated investments, net	$ (11.3)	$ (10.9)	$ (22.7)	$ (21.6)
WPL [Member]
Schedule of Equity Method Investments [Line Items]
Equity (income) loss from unconsolidated investments, net	(11.4)	(10.8)	(22.8)	(21.6)
ATC [Member]
Schedule of Equity Method Investments [Line Items]
Equity (income) loss from unconsolidated investments, net	(11.1)	(10.6)	(22.3)	(20.9)
ATC [Member] | WPL [Member]
Schedule of Equity Method Investments [Line Items]
Equity (income) loss from unconsolidated investments, net	(11.1)	(10.6)	(22.3)	(20.9)
Other [Member]
Schedule of Equity Method Investments [Line Items]
Equity (income) loss from unconsolidated investments, net	(0.2)	(0.3)	(0.4)	(0.7)
Other [Member] | WPL [Member]
Schedule of Equity Method Investments [Line Items]
Equity (income) loss from unconsolidated investments, net	(0.3)	(0.2)	(0.5)	(0.7)
Totals [Member]
Schedule of Equity Method Investments [Line Items]
Equity (income) loss from unconsolidated investments, net	(11.3)	(10.9)	(22.7)	(21.6)
Totals [Member] | WPL [Member]
Schedule of Equity Method Investments [Line Items]
Equity (income) loss from unconsolidated investments, net	$ (11.4)	$ (10.8)	$ (22.8)	$ (21.6)