Consolidated Statements of Comprehensive Income (Unaudited) (Parenthetical) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Other comprehensive (loss) income:
Income tax expense (benefit) on translation adjustments on net investment hedge	$ 1.7	$ (9.3)	$ 7.5	$ (31.0)
Income tax expense (benefit) on unrealized gain on investments		0.2		0.8
Income tax expense (benefit) on reclassification of unrealized cumulative gain on investments			(3.4)
Income tax expense (benefit) on defined benefit pension plans and retiree health care plan	$ 0.0	$ 0.1	$ 0.1	$ 0.3