Investments Loans by Debt Service Coverage Ratio (Details) (USD $) In Millions, unless otherwise specified	9 Months Ended
	Sep. 30, 2012		Dec. 31, 2011
Schedule of Loans by Debt Service Coverage Ratio [Line Items]
Total commercial mortgage loans	$ 2,909.8	[1]	$ 3,138.8	[1]
Greater than 1.5x
Schedule of Loans by Debt Service Coverage Ratio [Line Items]
Debt Service Coverage Ratio, minimum	150.00%
Total commercial mortgage loans	2,023.4	[1]	2,105.3	[1]
1.25x - 1.5x
Schedule of Loans by Debt Service Coverage Ratio [Line Items]
Debt Service Coverage Ratio, minimum	125.00%
Debt Service Coverage Ratio, maximum	150.00%
Total commercial mortgage loans	453.2	[1]	565.8	[1]
1.0x -1.25x
Schedule of Loans by Debt Service Coverage Ratio [Line Items]
Debt Service Coverage Ratio, minimum	100.00%
Debt Service Coverage Ratio, maximum	125.00%
Total commercial mortgage loans	285.0	[1]	355.5	[1]
Less than 1.0x
Schedule of Loans by Debt Service Coverage Ratio [Line Items]
Debt Service Coverage Ratio, minimum	0.00%
Debt Service Coverage Ratio, maximum	100.00%
Total commercial mortgage loans	$ 148.2	[1]	$ 112.2	[1]

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