Consolidated Balance Sheets (Parenthetical) (USD $) In Millions, except Share data, unless otherwise specified	Jun. 30, 2012	Dec. 31, 2011
Consolidated Balance Sheets [Abstract]
Fixed maturity securities investments, amortized cost	$ 16,444.1	$ 15,233.6
Equity securities investment, cost	847.2	937.7
Fixed maturity securities long-term investment, amortized cost	241.6	240.8
Equity securities long-term investment, cost	$ 26.8	$ 28.4
Preferred stock, par value	$ 0	$ 0
Preferred stock, shares authorized	100,000,000	100,000,000
Preferred stock, shares issued	0	0
Preferred stock, shares outstanding	0	0
Common stock, par value	$ 0.01	$ 0.01
Common stock, shares authorized	900,000,000	900,000,000
Common stock, shares issued	325,159,845	339,372,680
Common stock, shares outstanding	325,159,845	339,372,680