Allowance for Credit Losses (Narrative) (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012	Sep. 30, 2011	Dec. 31, 2011
Financing Receivable, Allowance for Credit Losses [Line Items]
Maximum Exposure Under First Loss Account	$ 30.7		$ 30.7		$ 34.3
Credit Enhancement Fees	1.0	1.1	3.0	3.5
Real Estate Acquired Through Foreclosure	9.9		9.9		9.8
Financing Receivable, Modifications, Payment Default Period			60 days
Banking on Business Loans [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Loss Given Default, Rate	100.00%		100.00%
Conventional Loan [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Troubled Debt Restructuring Modification Period			36 months
Troubled Debt Restructuring Modification, Housing Expense Ratio, Maximum	31.00%		31.00%
Troubled Debt Restructuring Loan Modification for Principal and Interest Payment Term, Maximum			40 years
Troubled Debt Restructuring Loan Modification Interest Rate Reduction Period if Expense Ratio is Not Met			36 months
Troubled Debt Restructuring Modification Incremental Interest Decrease Percent			0.125%
Troubled Debt Restructuring Modification Interest Decrease Floor, Percent			3.00%
Financing Receivable, Modifications, Recorded Investment	$ 6.0		$ 6.0