Consolidated Statements of Comprehensive Income - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014	Dec. 31, 2014
Statement of Income and Comprehensive Income [Abstract]
Net income	$ 452.8	$ 479.7	$ 1,022.8	$ 1,233.2
Other comprehensive income:
Foreign currency translation adjustments	(41.6)	(86.1)	(124.9)	(75.9)
Unrealized holding (loss)/gain on available-for-sale securities (net of taxes of $nil, $3.4 million, $nil and $1.3 million)	(2.0)	(7.2)	1.3	(3.5)
Comprehensive income	409.2	$ 386.4	899.2	$ 1,153.8
Components of accumulated other comprehensive income
Foreign currency translation adjustments	(150.6)		(150.6)		$ (25.7)
Unrealized holding loss on available-for-sale securities, net of taxes	(4.5)		(4.5)		(5.8)
Accumulated other comprehensive loss	$ (155.1)		$ (155.1)		$ (31.5)