Investments Loans by Loan to Value (Details) (USD $) In Millions, unless otherwise specified	Sep. 30, 2012		Dec. 31, 2011
Schedule of Loans by Loan to Value Ratio [Line Items]
Total commercial mortgage loans	$ 2,713.9	[1]	$ 2,374.8	[1]
0% - 50%
Schedule of Loans by Loan to Value Ratio [Line Items]
Total commercial mortgage loans	529.7	[1]	552.4	[1]
50% - 60%
Schedule of Loans by Loan to Value Ratio [Line Items]
Total commercial mortgage loans	793.2	[1]	771.5	[1]
60% - 70%
Schedule of Loans by Loan to Value Ratio [Line Items]
Total commercial mortgage loans	1,254.5	[1]	908.2	[1]
70% - 80%
Schedule of Loans by Loan to Value Ratio [Line Items]
Total commercial mortgage loans	120.3	[1]	125.2	[1]
80% and above
Schedule of Loans by Loan to Value Ratio [Line Items]
Total commercial mortgage loans	$ 16.2	[1]	$ 17.5	[1]

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