Consolidated Statements of Comprehensive Income (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2013	Mar. 31, 2012	Dec. 31, 2012
Statement of Income and Comprehensive Income [Abstract]
Net income	$ 64.8	$ 238.4
Other comprehensive income:
Foreign currency translation adjustments	(36.1)	36.6
Unrealized holding gain/(loss) on available-for-sale securities (net of taxes of $0.2 million and $nil)	(1.7)	2.9
Comprehensive income	27.0	277.9
Components of accumulated other comprehensive income
Foreign currency translation adjustments	49.0		85.1
Unrealized holding gain/(loss) on available-for-sale securities, net of taxes	0.1		1.8
Accumulated other comprehensive income	$ 49.1		$ 86.9