Consolidated Statements of Comprehensive Income (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2012	Mar. 31, 2011	Dec. 31, 2011
Statement of Income and Comprehensive Income [Abstract]
Net income	$ 238.4	$ 211.3
Other comprehensive income:
Foreign currency translation adjustments	36.6	70.6
Unrealized holding gain on available-for-sale securities (net of taxes of $nil and $2.3 million)	2.9	10.1
Other than temporary impairment of available-for-sale securities (net of taxes of $nil in all periods)	0	2.4
Comprehensive income	277.9	294.4
Components of accumulated other comprehensive income
Foreign currency translation adjustments	98.0		61.4
Unrealized holding gain/(loss) on available-for-sale securities, net of taxes	1.8		(1.1)
Accumulated other comprehensive income	$ 99.8		$ 60.3