Derivative Instruments Derivative Instruments Affecting the Consolidated Statements of Income (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Designated as Hedging Instrument [Member] | Cash Flow Hedging [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Amount of Gain (Loss) Recognized in OCI on Derivative (Effective Portion)	$ (3.8)	$ 0.0	$ (3.8)	$ 0.0
Amount of Ineffectiveness Recognized Related to Cash Flow Hedges	0.0		0.0
Designated as Hedging Instrument [Member] | Cash Flow Hedging [Member] | Treasury Lock Agreements [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Amount of Gain (Loss) Recognized in OCI on Derivative (Effective Portion)	(3.8)	0.0	(3.8)	0.0
Not Designated as Hedging Instrument [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Amount of Gain/(Loss) Recognized in Income on Derivative	8.3	(18.0)	42.2	(19.7)
Not Designated as Hedging Instrument [Member] | Foreign Currency Forward Contracts [Member] | Foreign Exchange Gain (Loss) [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Amount of Gain/(Loss) Recognized in Income on Derivative	0.0	(18.0)	(11.9)	(15.8)
Not Designated as Hedging Instrument [Member] | Foreign Currency Zero-Cost Collar Contracts [Member] | Foreign Exchange Gain (Loss) [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Amount of Gain/(Loss) Recognized in Income on Derivative	$ 8.3	$ 0.0	$ 54.1	$ (3.9)