Derivatives Additional information (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2015		Mar. 31, 2014		Oct. 17, 2012	Dec. 31, 2014	May 31, 2013	Jan. 17, 2011
Derivative Instruments, Gain (Loss) [Line Items]
Derivative, Number of Instruments Held	10				4
Other Expense
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) on Cash Flow Hedge Ineffectiveness, Net	$ (2.3)		$ 0
Interest Rate Swap
Derivative Instruments, Gain (Loss) [Line Items]
Derivative, Number of Instruments Held							6
Weighted average fixed rate paid	3.57%				3.391%	3.57%		4.553%
Derivative, Lower Fixed Interest Rate Range							1.026%
Derivative, Higher Fixed Interest Rate Range							1.04%
Derivative, Basis Spread on Fixed Rate							2.75%
Derivative, Basis Spread on Variable Rate							0.75%
Variable rate received	0.17%					0.16%
Debt Instrument, Credit Rating	A
August 21, 2012 Transaction Date [Domain]
Derivative Instruments, Gain (Loss) [Line Items]
Notional Amount of Interest Rate Cash Flow Hedge Derivatives	900.0
May 31, 2013 Transaction Date [Domain]
Derivative Instruments, Gain (Loss) [Line Items]
Notional Amount of Interest Rate Cash Flow Hedge Derivatives	750.0
Designated as Hedging Instrument [Member] | Interest Rate Swap | Other Comprehensive Income (Loss)
Derivative Instruments, Gain (Loss) [Line Items]
Changes in fair value of effective portion, net of tax (a)	(5.2)	[1]	(4.3)	[1]
De-Designated Hedging Instrument [Member] | Interest Rate Swap
Derivative Instruments, Gain (Loss) [Line Items]
Interest Rate Cash Flow Hedge Gain (Loss) to be Reclassified During Next 12 Months, Net	(5.0)
De-Designated Hedging Instrument [Member] | Interest Rate Swap | Other Comprehensive Income (Loss)
Derivative Instruments, Gain (Loss) [Line Items]
Amortization of unrealized losses on de-designated interest rate swaps, net of tax (a)	2.0	[1]	2.6	[1]
Other Assets [Member] | Designated as Hedging Instrument [Member] | Interest Rate Swap
Derivative Instruments, Gain (Loss) [Line Items]
Interest Rate Cash Flow Hedge Derivative at Fair Value, Net	0					0.4
Other current liabilities | Designated as Hedging Instrument [Member] | Interest Rate Swap
Derivative Instruments, Gain (Loss) [Line Items]
Interest Rate Cash Flow Hedge Derivative at Fair Value, Net	28.5					28.5
Other noncurrent liabilities | Designated as Hedging Instrument [Member] | Interest Rate Swap
Derivative Instruments, Gain (Loss) [Line Items]
Interest Rate Cash Flow Hedge Derivative at Fair Value, Net	54.7					48.7
Accumulated Other Comprehensive Income | Designated as Hedging Instrument [Member] | Interest Rate Swap
Derivative Instruments, Gain (Loss) [Line Items]
Interest Rate Cash Flow Hedge Derivative at Fair Value, Net	(3.7)					4.9
Accumulated Other Comprehensive Income | De-Designated Hedging Instrument [Member] | Interest Rate Swap
Derivative Instruments, Gain (Loss) [Line Items]
Interest Rate Cash Flow Hedge Derivative at Fair Value, Net	$ (5.5)					(8.8)

[1] Included as a component of other comprehensive loss and will be reclassified into earnings as the hedged transaction affects earnings.