Derivative Instruments Cash Flow Hedges (Details) - Foreign Exchange Contract - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Cash flows, revenue | Revenue
Summary of the effect of derivatives designated as hedging instruments on the consolidated statements of income
Net gains (losses) in operating income for the settlement of certain effective cash flow hedge instruments	$ (42.5)	$ (32.5)	$ 5.3
Net gains (losses) in net income of foreign currency forward contracts due to exclusion from effectiveness testing	10.8
Cash flows, revenue | Other income (expense)
Summary of the effect of derivatives designated as hedging instruments on the consolidated statements of income
Net gains (losses) in net income of foreign currency forward contracts due to exclusion from effectiveness testing		8.9	2.9
Cash flows, operating expenses | Other income (expense)
Summary of the effect of derivatives designated as hedging instruments on the consolidated statements of income
Net gains (losses) in net income of foreign currency forward contracts due to exclusion from effectiveness testing		(0.2)	0.1
Cash flows, operating expenses | Operating Expense
Summary of the effect of derivatives designated as hedging instruments on the consolidated statements of income
Net gains (losses) in operating income for the settlement of certain effective cash flow hedge instruments	0.2	$ 0.6	$ (1.5)
Net gains (losses) in net income of foreign currency forward contracts due to exclusion from effectiveness testing	$ (0.1)