Derivative Instruments Fair Value of Derivative Instruments (Details) - USD ($) $ in Millions	Sep. 30, 2017	Dec. 31, 2016
Derivatives, Fair Value [Line Items]
Derivative assets, fair value	$ 18.8	$ 0.0
Derivative liabilities, fair value	4.6	41.1
Not Designated as Hedging Instrument [Member]
Derivatives, Fair Value [Line Items]
Derivative assets, fair value	18.8	0.0
Derivative liabilities, fair value	0.0	41.1
Not Designated as Hedging Instrument [Member] | Foreign Currency Zero-Cost Collar Contracts [Member] | Other Current Assets [Member]
Derivatives, Fair Value [Line Items]
Derivative assets, fair value	18.8	0.0
Not Designated as Hedging Instrument [Member] | Foreign Currency Forward Contracts [Member] | Accounts Payable and Accrued Liabilities [Member]
Derivatives, Fair Value [Line Items]
Derivative liabilities, fair value	0.0	41.1
Designated as Hedging Instrument [Member]
Derivatives, Fair Value [Line Items]
Derivative liabilities, fair value	4.6	0.0
Designated as Hedging Instrument [Member] | Treasury Lock Agreements [Member] | Other Noncurrent Liabilities and Deferred Credits [Member]
Derivatives, Fair Value [Line Items]
Derivative liabilities, fair value	$ 4.6	$ 0.0