Derivative Instruments Summary of Foreign Currency Derivative Contracts (Details) $ in Millions, $ in Millions		6 Months Ended		12 Months Ended
	Jan. 17, 2017 USD ($)	Jun. 30, 2018 USD ($) $ / $	Jun. 30, 2017 USD ($)	Dec. 31, 2017 USD ($)		Jan. 17, 2017 MXN ($) $ / $	Jan. 17, 2017 USD ($) $ / $
Derivative [Line Items]
Cash received/(paid) on settlement of foreign currency contracts		$ 12.0	$ (23.7)
Not Designated as Hedging Instrument [Member] | Foreign Currency Forward Contracts [Member]
Derivative [Line Items]
Notional amount of foreign currency contracts						$ 6,207.7	$ 340.0
Weighted-average exchange rate of foreign currency forward contracts | $ / $						18.3	18.3
Maturity date of foreign currency forward contracts	Jan. 17, 2017
Not Designated as Hedging Instrument [Member] | Foreign Currency Forward Contracts [Member] | Foreign Exchange Gain (Loss) [Member]
Derivative [Line Items]
Cash received/(paid) on settlement of foreign currency contracts	$ (53.0)
Not Designated as Hedging Instrument [Member] | Foreign Currency Forward Contracts [Member] | Offsetting Derivative Instrument [Member]
Derivative [Line Items]
Notional amount of foreign currency contracts						$ 6,207.7	$ 287.0
Weighted-average exchange rate of foreign currency forward contracts | $ / $						21.6	21.6
Maturity date of foreign currency forward contracts	Jan. 17, 2017
Not Designated as Hedging Instrument [Member] | Foreign Currency Zero-Cost Collar Contracts [Member]
Derivative [Line Items]
Notional amount of foreign currency contracts		$ 215.0
Not Designated as Hedging Instrument [Member] | Foreign Currency Zero-Cost Collar Contracts [Member] | Call Option [Member]
Derivative [Line Items]
Weighted-average rate outstanding options | $ / $		19.3
Not Designated as Hedging Instrument [Member] | Foreign Currency Zero-Cost Collar Contracts [Member] | Put Option [Member]
Derivative [Line Items]
Weighted-average rate outstanding options | $ / $		22.2
Not Designated as Hedging Instrument [Member] | Foreign Currency Zero-Cost Collar Contracts [Member] | Contracts Executed in 2018 and Settled in 2018 [Member]
Derivative [Line Items]
Notional amount of foreign currency contracts		$ 125.0
Not Designated as Hedging Instrument [Member] | Foreign Currency Zero-Cost Collar Contracts [Member] | Contracts Executed in 2018 and Settled in 2018 [Member] | Foreign Exchange Gain (Loss) [Member]
Derivative [Line Items]
Cash received/(paid) on settlement of foreign currency contracts		2.0
Not Designated as Hedging Instrument [Member] | Foreign Currency Zero-Cost Collar Contracts [Member] | Contracts Executed in 2017 and Settled in 2018 [Member]
Derivative [Line Items]
Notional amount of foreign currency contracts				$ 80.0
Not Designated as Hedging Instrument [Member] | Foreign Currency Zero-Cost Collar Contracts [Member] | Contracts Executed in 2017 and Settled in 2018 [Member] | Foreign Exchange Gain (Loss) [Member]
Derivative [Line Items]
Cash received/(paid) on settlement of foreign currency contracts		$ 10.0
Not Designated as Hedging Instrument [Member] | Foreign Currency Zero-Cost Collar Contracts [Member] | Contracts Executed in 2017 and Settled in 2017 [Member]
Derivative [Line Items]
Notional amount of foreign currency contracts			310.0	450.0	[1]
Not Designated as Hedging Instrument [Member] | Foreign Currency Zero-Cost Collar Contracts [Member] | Contracts Executed in 2017 and Settled in 2017 [Member] | Foreign Exchange Gain (Loss) [Member]
Derivative [Line Items]
Cash received/(paid) on settlement of foreign currency contracts			$ 29.3	$ 42.2	[1]

[1] During the first half of 2017, the Company settled $310.0 million of zero-cost collar contracts, resulting in cash received of $29.3 million.