Consolidated Statements Of Comprehensive Income (Unaudited) (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
Other comprehensive income (loss):
Income tax expense (benefit) on unrealized gain (loss) on investments	$ (0.3)	$ (0.2)	$ 0.5	$ 0.1
Income tax expense (benefit) on amortization of net loss (gain) included in net periodic benefit cost	$ 0	$ 0.1	$ 0.1	$ 0.3