Condensed Consolidated Balance Sheets Condensed Consolidated Balance Sheets Parenthetical (USD $) In Millions, except Share data, unless otherwise specified	Jun. 30, 2012	Dec. 31, 2011
Statement of Financial Position [Abstract]
Fixed maturities, amortized costs	$ 17,095.2	$ 16,577.9
Equity securities, cost	131.2	131.8
Securities pledged, amortized costs	$ 342.2	$ 572.5
Common stock, par value	$ 50.00	$ 50.00
Common stock, shares authorized	100,000	100,000
Common stock, shares issued	55,000	55,000
Common stock, shares outstanding	55,000	55,000