Sensitivity of the Current Fair Value of Residual Cash Flows to Immediate 10% and 20% Adverse Changes in Assumptions (Detail) (USD $)	Mar. 31, 2012
Fixed Rate Residential Mortgage
Sensitivity Analysis of Fair Value of Interests Continued to be Held by Transferor, Servicing Assets or Liabilities, Impact of Adverse Change in Assumption [Line Items]
Fair Value	$ 732,000,000
Weighted- Average Life (in years)	5.4
Rate	14.40%
Impact of Adverse Change on Fair Value 10%	(37,000,000)
Impact of Adverse Change on Fair Value 20%	(70,000,000)
Discount Rate	10.60%
Impact of Adverse Change on Fair Value 10%	(27,000,000)
Impact of Adverse Change on Fair Value 20%	(51,000,000)
Adjustable Rate Residential Mortgage
Sensitivity Analysis of Fair Value of Interests Continued to be Held by Transferor, Servicing Assets or Liabilities, Impact of Adverse Change in Assumption [Line Items]
Fair Value	35,000,000
Weighted- Average Life (in years)	3.1
Rate	26.50%
Impact of Adverse Change on Fair Value 10%	(2,000,000)
Impact of Adverse Change on Fair Value 20%	(3,000,000)
Discount Rate	11.80%
Impact of Adverse Change on Fair Value 10%	(1,000,000)
Impact of Adverse Change on Fair Value 20%	$ (2,000,000)