Consolidated Statements of Comprehensive Income (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2014	Mar. 31, 2013	Dec. 31, 2013
Statement of Income and Comprehensive Income [Abstract]
Net income	$ 230.4	$ 64.8
Other comprehensive income:
Foreign currency translation adjustments	(1.7)	(36.1)
Unrealized holding gain on available-for-sale securities (net of taxes of $2.5 million and $0.2 million)	4.3	(1.7)
Comprehensive income	233.0	27.0
Components of accumulated other comprehensive income
Foreign currency translation adjustments	108.7		110.4
Unrealized holding gain/(loss) on available-for-sale securities, net of taxes	4.1		(0.2)
Accumulated other comprehensive income	$ 112.8		$ 110.2