Condensed Consolidated Balance Sheets Parenthetical (USD $) In Millions, except Share data, unless otherwise specified	Dec. 31, 2012	Dec. 31, 2011
Statement of Financial Position [Abstract]
Fixed maturities, amortized cost	$ 18,458.7	$ 16,577.9
Equity securities, cost	129.3	131.8
Mortgage loans on real estate valuation allowance	1.3	1.3
Securities pledged, amortized costs	$ 207.2	$ 572.5
Common stock, par value	$ 50	$ 50
Common stock, shares authorized	100,000	100,000
Common stock, shares issued	55,000	55,000
Common stock, shares outstanding	55,000	55,000