Consolidated Statements of Comprehensive Income - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Dec. 31, 2017
Statement of Comprehensive Income [Abstract]
Net income	$ 550.6	$ 375.0
Other comprehensive income:
Foreign currency translation adjustments	539.5	265.5
Pension and other employee benefits (net of tax benefit of $nil and $0.4 million for the three months ended March 31, 2018 and 2017, respectively)	(0.5)	7.4
Unrealized (loss)/gain on available-for-sale securities (net of tax expense of $nil and $2.2 million for the three months ended March 31, 2018 and 2017, respectively)	(67.9)	2.1
Hedging activities (net of tax benefit of $nil and $2.7 million for the three months ended March 31, 2018 and 2017, respectively)	0.0	(4.5)
Comprehensive income	1,021.7	$ 645.5
Components of accumulated other comprehensive loss
Foreign currency translation adjustments	1,819.1		$ 1,279.6
Pension and other employee benefits, net of taxes	27.0		27.5
Unrealized holding gain on available-for-sale securities, net of taxes	0.0		67.9
Accumulated other comprehensive income	$ 1,846.1		$ 1,375.0