Summary of Significant Valuation Assumptions for AFS Securities (Detail)	Jun. 30, 2011
Residential Prime | Minimum
Schedule of Available-for-sale Securities [Line Items]
Prepayment rates	4.00%
Loss severity	14.00%
Projected losses	0.00%
Residential Prime | Maximum
Schedule of Available-for-sale Securities [Line Items]
Prepayment rates	15.00%
Loss severity	57.00%
Projected losses	26.00%
Residential non-prime | Minimum
Schedule of Available-for-sale Securities [Line Items]
Prepayment rates	1.00%
Loss severity	22.00%
Projected losses	1.00%
Residential non-prime | Maximum
Schedule of Available-for-sale Securities [Line Items]
Prepayment rates	8.00%
Loss severity	57.00%
Projected losses	39.00%
Commercial | Minimum
Schedule of Available-for-sale Securities [Line Items]
Loss severity	33.00%
Projected losses	2.00%
Commercial | Maximum
Schedule of Available-for-sale Securities [Line Items]
Loss severity	50.00%
Projected losses	7.00%