Consolidated Statements of Comprehensive Income (Parenthetical) (USD $) In Millions, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012	Sep. 30, 2011
Statement of Income and Comprehensive Income [Abstract]
Unrealized holding gain/(loss) on available-for-sale securities (net of taxes of $0.8 million, $0.3 million, $3.7 million and $0.2 million)	$ 0.8	$ 0.3	$ 3.7	$ 0.2
Other than temporary impairment of available-for-sale securities (net of taxes of $nil in all periods)	0	0	0	0
Realized gain on divestment of available-for-sale securities (net of taxes of $nil, $3.5 million, $nil and $3.5 million)	$ 0	$ 3.5	$ 0	$ 3.5