Consolidated Statements of Comprehensive Income/(Loss) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015	Dec. 31, 2015
Statement of Comprehensive Income [Abstract]
Net (loss)/income	$ (386.8)	$ 452.8	$ (129.9)	$ 1,022.8
Other comprehensive (loss)/income:
Foreign currency translation adjustments	234.3	(41.6)	38.8	(124.9)
Unrealized gain/(loss) on available-for-sale securities (net of tax expense of $2.4 and $1.0 for the three and nine months ended September 30, 2016 and $nil for both the three and nine months ended September 30, 2015)	15.1	(2.0)	10.4	1.3
Hedging activities, net of tax expense of $1.2 and tax benefit of $0.5 for the three and nine months ended September 30, 2016, respectively and $nil for both the three and nine months ended September 30, 2015	2.2	0.0	0.4	0.0
Comprehensive (loss)/income	(135.2)	$ 409.2	(80.3)	$ 899.2
Components of accumulated other comprehensive income
Foreign currency translation adjustments	(143.3)		(143.3)		$ (182.1)
Unrealized holding gain/(loss) on available-for-sale securities, net of taxes	8.7		8.7		(1.7)
Hedging activities, net of taxes	0.4		0.4		0.0
Accumulated other comprehensive loss	$ (134.2)		$ (134.2)		$ (183.8)