Consolidated Statements of Comprehensive Income (USD $) In Millions, unless otherwise specified	3 Months Ended		12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Statement of Income and Comprehensive Income [Abstract]
Net income	$ 42.0	$ 255.3	$ 745.4	$ 865.0	$ 588.0
Other comprehensive income:
Foreign currency translation adjustments			23.7	(24.0)	(51.3)
Unrealized holding gain/(loss) on available-for-sale securities (net of taxes of $2.5 million, $0.2 million, and $nil)			2.9	16.2	(13.6)
Other than temporary impairment of available-for-sale securities (net of taxes of $nil in all periods)			0	2.4	1.5
Realized gain on divestment of available-for-sale securities (net of taxes of $nil, $3.5 million and $nil)			0	(20.0)	0
Comprehensive income			772.0	839.6	524.6
Components of accumulated other comprehensive income
Foreign currency translation adjustments	85.1	61.4	85.1	61.4
Unrealized holding gain/(loss) on available-for-sale securities, net of taxes	1.8	(1.1)	1.8	(1.1)
Accumulated other comprehensive income	$ 86.9	$ 60.3	$ 86.9	$ 60.3