Investments - Loans by Loan to Value (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2014		Dec. 31, 2013
Schedule of Loans by Loan to Value Ratio [Line Items]
Benchmark loan to value ratio, greater than indicates unpaid loan amount exceeds underlying collateral	100.00%
Loans Receivable, Gross, Commercial, Real Estate	$ 3,378.2	[1]	$ 3,397.3	[1]
0% - 50%
Schedule of Loans by Loan to Value Ratio [Line Items]
Loan to Value Ratio, minimum	0.00%
Loan to Value Ratio, maximum	50.00%
Total commercial mortgage loans	440.6	[1]	495.7	[1]
50% - 60%
Schedule of Loans by Loan to Value Ratio [Line Items]
Loan to Value Ratio, minimum	50.00%
Loan to Value Ratio, maximum	60.00%
Total commercial mortgage loans	920.9	[1]	894.5	[1]
60% - 70%
Schedule of Loans by Loan to Value Ratio [Line Items]
Loan to Value Ratio, minimum	60.00%
Loan to Value Ratio, maximum	70.00%
Total commercial mortgage loans	1,891.2	[1]	1,879.5	[1]
70% - 80%
Schedule of Loans by Loan to Value Ratio [Line Items]
Loan to Value Ratio, minimum	70.00%
Loan to Value Ratio, maximum	80.00%
Total commercial mortgage loans	113.1	[1]	114.9	[1]
80% and above
Schedule of Loans by Loan to Value Ratio [Line Items]
Loan to Value Ratio, minimum	80.00%
Total commercial mortgage loans	$ 12.4	[1]	$ 12.7	[1]

[1] Balances do not include allowance for mortgage loan credit losses.