Condensed Consolidated Balance Sheets Parenthetical - USD ($) $ in Millions	Jun. 30, 2015	Dec. 31, 2014
Statement of Financial Position [Abstract]
Fixed maturities, amortized cost	$ 19,551.7	$ 19,085.0
Equity securities, cost	106.6	107.4
Mortgage loans on real estate valuation allowance	1.1	1.1
Securities pledged, amortized costs	$ 176.2	$ 224.4
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