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 Other Comprehensive Income [Abstract]
(1) Tax expense of unrealized holding gains on securities	$ 3.0	$ 26.7	$ 8.8	$ 38.0
(2) Tax benefit of reclassification adjustment for gains included in net income	$ 1.8	$ 0.2	$ 2.1	$ 1.7