Underwriting Acquisition And Insurance Expenses (Underwriting, Acquisition And Insurance Expenses) (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012	Sep. 30, 2011
Commissions	$ 55.3	$ 49.0	$ 156.0	$ 143.1
General expenses	60.2	51.0	182.2	153.1
Premium taxes, boards and bureaus	7.1	8.0	19.2	19.7
Total Underwriting Acquisition And Insurance Expenses, Total	122.6	108.0	357.4	315.9
Net deferral of policy acquisition costs	(4.6)	(3.8)	(11.1)	(1.2)
Total underwriting, acquisition and insurance expenses	$ 118.0	$ 104.2	$ 346.3	$ 314.7