Condensed Balance Sheets Parenthetical (USD $) In Millions, except Share data, unless otherwise specified	Sep. 30, 2012	Dec. 31, 2011
Statement of Financial Position [Abstract]
Fixed maturities - amortized cost	$ 18,941.5	$ 20,062.4
Equity securities cost	26.5	26.7
Mortgage loans on real estate valuation allowance	1.4	1.5
Securities pledged - amortized cost	$ 619.3	$ 965.0
Common Stock, shares authorized	250,000	250,000
Common stock, shares issued	250,000	250,000
Common stock, shares outstanding	250,000	250,000
Common stock, per share value (in dollars per share)	$ 10.00	$ 10.00