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 Other Comprehensive Income [Abstract]
(1) Net of income tax expense of unrealized holding gains/(losses) on securities	$ 5.8	$ 14.8	$ 5.8	$ 11.3
(2) Net of income tax benefit of reclassification adjustment for gains included in net income	$ 0.1	$ 0.3	$ 0.3	$ 1.5