Fair Values of Assets and Liabilities - Valuation Assumption Ranges for Level 3 Available -for-Sale Investment Securities (Detail)	Jun. 30, 2014
Minimum [Member] | Non-agency Prime [Member] | Mortgage-backed securities Residential [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Estimated lifetime prepayment rates	6.00%
Lifetime probability of default rates	0.00%
Lifetime loss severity rates	15.00%
Discount margin	2.00%
Minimum [Member] | Non-agency Non-prime [Member] | Mortgage-backed securities Residential [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Estimated lifetime prepayment rates	1.00%
Lifetime probability of default rates	4.00%
Lifetime loss severity rates	15.00%
Discount margin	1.00%
Minimum [Member] | Asset-Backed Securities [Member] | Asset-backed securities Other [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Estimated lifetime prepayment rates	6.00%
Lifetime probability of default rates	5.00%
Lifetime loss severity rates	40.00%
Discount margin	6.00%
Maximum [Member] | Non-agency Prime [Member] | Mortgage-backed securities Residential [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Estimated lifetime prepayment rates	20.00%
Lifetime probability of default rates	7.00%
Lifetime loss severity rates	75.00%
Discount margin	5.00%
Maximum [Member] | Non-agency Non-prime [Member] | Mortgage-backed securities Residential [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Estimated lifetime prepayment rates	10.00%
Lifetime probability of default rates	12.00%
Lifetime loss severity rates	75.00%
Discount margin	5.00%
Maximum [Member] | Asset-Backed Securities [Member] | Asset-backed securities Other [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Estimated lifetime prepayment rates	6.00%
Lifetime probability of default rates	5.00%
Lifetime loss severity rates	40.00%
Discount margin	6.00%
Average [Member] | Non-agency Prime [Member] | Mortgage-backed securities Residential [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Estimated lifetime prepayment rates	14.00%
Lifetime probability of default rates	4.00%
Lifetime loss severity rates	38.00%
Discount margin	3.00%
Average [Member] | Non-agency Non-prime [Member] | Mortgage-backed securities Residential [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Estimated lifetime prepayment rates	6.00%
Lifetime probability of default rates	8.00%
Lifetime loss severity rates	54.00%
Discount margin	2.00%
Average [Member] | Asset-Backed Securities [Member] | Asset-backed securities Other [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Estimated lifetime prepayment rates	6.00%
Lifetime probability of default rates	5.00%
Lifetime loss severity rates	40.00%
Discount margin	6.00%