Consolidated Statements of Comprehensive Income - USD ($) $ in Millions	3 Months Ended		12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Statement of Comprehensive Income [Abstract]
Net income	$ 3,105.4	$ 457.3	$ 4,271.5	$ 327.4	$ 1,303.4
Other comprehensive income/(loss):
Foreign currency translation adjustments			2,785.0	(1,323.3)	(156.4)
Pension and other employee benefits (net of tax expense of $11.2 million, $8.8 million and $nil for the years ended December 31, 2017, 2016 and 2015, respectively)			32.7	(5.2)	0.0
Unrealized gain on available-for-sale securities (net of tax benefit of $0.1 million the years ended December 31, 2017 and 2016 and $nil for the year ended December 31, 2015)			61.3	8.3	4.1
Hedging activities (net of tax benefit of $3.1 million, tax expense of $3.3 million and $nil for the years ended December 31, 2017, 2016 and 2015, respectively)			(6.4)	6.4	0.0
Comprehensive income/(loss)			7,144.1	(986.4)	$ 1,151.1
Components of accumulated other comprehensive loss
Foreign currency translation adjustments	1,279.6	(1,505.4)	1,279.6	(1,505.4)
Pension and other employee benefits, net of taxes	27.5	(5.2)	27.5	(5.2)
Unrealized holding gain on available-for-sale securities, net of taxes	67.9	6.6	67.9	6.6
Hedging activities, net of taxes	0.0	6.4	0.0	6.4
Accumulated other comprehensive income/(loss)	$ 1,375.0	$ (1,497.6)	$ 1,375.0	$ (1,497.6)