Financial Instruments (Summary of Derivative Instruments) (Details) - USD ($) $ in Millions	9 Months Ended	12 Months Ended
	Sep. 30, 2017	Dec. 31, 2016
Undesignated derivative instruments | Foreign Exchange Contract
Derivative [Line Items]
Notional amount	$ 1,514.6	$ 1,309.1
Maximum duration (in months)	3 months	3 months
Fair value - net asset	$ 7.6	$ 6.7
Designated derivative Instruments | Foreign Exchange Contract
Derivative [Line Items]
Notional amount		78.7
Maximum duration (in months)	6 months
Fair value - net asset		4.2
Designated derivative Instruments | Interest Rate Swap | Fair Value Hedging
Derivative [Line Items]
Notional amount	$ 1,000.0	1,000.0
Fair value - net asset	$ 0.6	$ (1.2)