CONSOLIDATED BALANCE SHEETS (Parenthetical) (USD $) In Millions, except Per Share data, unless otherwise specified	Sep. 30, 2012	Dec. 31, 2011
Fixed maturities, amortized cost	$ 6,363.6	$ 6,008.7
Equity securities, cost	$ 363.0	$ 239.9
Preferred stock, par value	$ 0.01	$ 0.01
Preferred stock, shares authorized	20.0	20.0
Preferred stock, issued
Common stock, par value	$ 0.01	$ 0.01
Common stock, shares authorized	300.0	300.0
Common stock, shares issued	60.5	60.5
Treasury stock, shares	16.2	15.9