Consolidated Statements of Comprehensive Income - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017	Dec. 31, 2017
Statement of Comprehensive Income [Abstract]
Net income	$ 537.2	$ 550.8	$ 1,703.3	$ 1,166.1
Other comprehensive income:
Foreign currency translation adjustments	(100.7)	744.6	(679.2)	2,441.1
Pension and other employee benefits (net of tax expense of $nil for the three and nine months ended September 30, 2018 and $nil and $0.9 for the three and nine months ended September 30, 2017, respectively)	(0.5)	0.4	(1.5)	11.0
Unrealized gain on available-for-sale securities (net of tax expense of $nil for the three and nine months ended September 30, 2018 and $5.5 and $7.2 for the three and nine months ended September 30, 2017, respectively)	0.0	23.8	(67.9)	20.3
Hedging activities (net of tax benefit of $nil for the three and nine months ended September 30, 2018 and $nil and $3.2 for the three and nine months ended September 30, 2017, respectively)	0.0	0.2	0.0	(5.7)
Comprehensive income	436.0	$ 1,319.8	954.7	$ 3,632.8
Components of accumulated other comprehensive loss
Foreign currency translation adjustments	600.4		600.4		$ 1,279.6
Pension and other employee benefits, net of taxes	26.0		26.0		27.5
Unrealized holding gain on available-for-sale securities, net of taxes	0.0		0.0		67.9
Accumulated other comprehensive income	$ 626.4		$ 626.4		$ 1,375.0