Income Taxes - Unrecognized Tax Benefits (Details 7) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Reconciliation of Unrecognized Tax Benefits
Balance at beginning of year	$ 53.8	$ 54.0	$ 49.2
Increases (decreases) for prior year tax positions	(0.2)	(0.8)	1.6
Increases (decreases) for current year tax positions	7.7	0.9	3.7
Decreases related to statute lapse	(1.4)	(0.3)	(0.5)
Balance at end of year	59.9	53.8	54.0
Significant Change in Unrecognized Tax Benefits is Reasonably Possible, Amount of Unrecorded Benefit	0
Unrecognized Tax Benefits that Would Impact Effective Tax Rate	41.6	42.6
Unrecognized tax benefits that would result in adjustments to other tax accounts	18.4	11.2
Unrecognized tax benefits, accrued interest and penalties	$ 0.3	$ 0.7
Earliest Tax Year [Member] | Domestic Tax Authority [Member]
Income Tax Contingency [Line Items]
Open Tax Year by Major Tax Jurisdiction	2011
Earliest Tax Year [Member] | State and Local Jurisdiction [Member]
Income Tax Contingency [Line Items]
Open Tax Year by Major Tax Jurisdiction	2007