Condensed Consolidated Balance Sheets Parenthetical (USD $) In Millions, except Share data, unless otherwise specified	Sep. 30, 2013	Dec. 31, 2012
Statement of Financial Position [Abstract]
Fixed maturities, amortized cost	$ 19,018.1	$ 18,458.7
Equity securities, cost	111.2	129.3
Mortgage loans on real estate valuation allowance	1.4	1.3
Securities pledged, amortized costs	$ 178.0	$ 207.2
Common stock, par value	$ 50.0	$ 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