Financial Instruments Loans by Debt Service Coverage Ratio (Details) (USD $) In Millions, unless otherwise specified	6 Months Ended
	Jun. 30, 2012		Dec. 31, 2011
Schedule of Loans by Debt Service Coverage Ratio [Line Items]
Total commercial mortgage loans	$ 2,711.5	[1]	$ 2,374.8	[1]
Mortgages secured by loans on land or construction loans
Schedule of Loans by Debt Service Coverage Ratio [Line Items]
Total commercial mortgage loans	0	[1]	0	[1]
Greater than 1.5x
Schedule of Loans by Debt Service Coverage Ratio [Line Items]
Total commercial mortgage loans	1,956.6	[1]	1,600.1	[1]
Debt Service Coverage Ratio, minimum	150.00%
1.25x - 1.5x
Schedule of Loans by Debt Service Coverage Ratio [Line Items]
Total commercial mortgage loans	397.5	[1]	408.1	[1]
Debt Service Coverage Ratio, minimum	125.00%
Debt Service Coverage Ratio, maximum	150.00%
1.0x - 1.25x
Schedule of Loans by Debt Service Coverage Ratio [Line Items]
Total commercial mortgage loans	280.9	[1]	286.7	[1]
Debt Service Coverage Ratio, minimum	100.00%
Debt Service Coverage Ratio, maximum	125.00%
Less than 1.0x
Schedule of Loans by Debt Service Coverage Ratio [Line Items]
Total commercial mortgage loans	$ 76.5	[1]	$ 79.9	[1]
Debt Service Coverage Ratio, minimum	0.00%
Debt Service Coverage Ratio, maximum	100.00%

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