Other-Than-Temporary Impairment (Significant Inputs for OTTI) (Details) (Residential Mortgage Backed Securities [Member])	9 Months Ended
	Sep. 30, 2012
Other than Temporary Impairment, Disclosure [Line Items]
Prepayment Rates, Weighted Avg	10.80%
Default Rates, Weighted Avg	27.20%
Loss Severities, Weighted Avg	44.00%
Current Credit Enhancement, Weighted Avg	2.60%
Prime [Member] | Securitization in 2006 [Member]
Other than Temporary Impairment, Disclosure [Line Items]
Prepayment Rates, Weighted Avg	9.80%
Default Rates, Weighted Avg	19.80%
Loss Severities, Weighted Avg	36.20%
Current Credit Enhancement, Weighted Avg	5.50%
Alt-A [Member] | Securitization in 2006 [Member]
Other than Temporary Impairment, Disclosure [Line Items]
Prepayment Rates, Weighted Avg	11.00%
Default Rates, Weighted Avg	29.40%
Loss Severities, Weighted Avg	46.30%
Current Credit Enhancement, Weighted Avg	1.70%
Maximum [Member]
Other than Temporary Impairment, Disclosure [Line Items]
Prepayment Rates, Range	13.10%
Default Rates, Range	39.30%
Loss Severities, Range	49.20%
Current Credit Enhancement, Range	5.50%
Maximum [Member] | Prime [Member] | Securitization in 2006 [Member]
Other than Temporary Impairment, Disclosure [Line Items]
Prepayment Rates, Range	9.80%
Default Rates, Range	19.80%
Loss Severities, Range	36.20%
Current Credit Enhancement, Range	5.50%
Maximum [Member] | Alt-A [Member] | Securitization in 2006 [Member]
Other than Temporary Impairment, Disclosure [Line Items]
Prepayment Rates, Range	13.10%
Default Rates, Range	39.30%
Loss Severities, Range	49.20%
Current Credit Enhancement, Range	3.30%
Minimum [Member]
Other than Temporary Impairment, Disclosure [Line Items]
Prepayment Rates, Range	8.80%
Default Rates, Range	19.80%
Loss Severities, Range	36.20%
Current Credit Enhancement, Range	0.00%
Minimum [Member] | Alt-A [Member] | Securitization in 2006 [Member]
Other than Temporary Impairment, Disclosure [Line Items]
Prepayment Rates, Range	8.80%
Default Rates, Range	20.20%
Loss Severities, Range	43.60%
Current Credit Enhancement, Range	0.00%