Consolidated Statements of Comprehensive Income (Parenthetical) (USD $) In Millions, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2012	Jun. 30, 2011	Jun. 30, 2012	Jun. 30, 2011
Statement of Income and Comprehensive Income [Abstract]
Unrealized holding gain on available-for-sale securities (net of taxes of $2.9 million, $1.1 million, $2.9 million and $3.4 million)	$ 2.9	$ 1.1	$ 2.9	$ 3.4
Other than temporary impairment of available-for-sale securities (net of taxes of $nil in all periods)	$ 0	$ 0	$ 0	$ 0