Condensed Consolidated Balance Sheets Parenthetical - USD ($) $ in Millions	Dec. 31, 2016	Dec. 31, 2015
Statement of Financial Position [Abstract]
Fixed maturities, amortized cost	$ 22,364.8	$ 20,747.1
Equity securities, cost	67.1	116.7
Mortgage loans on real estate valuation allowance	1.1	1.2
Securities pledged, amortized costs	$ 692.8	$ 252.3
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