Mortgage Servicing Rights - Sensitivity to Changes in Interest Rates of the Fair Value of MSRs Portfolio and Related Derivative Instruments (Detail) - USD ($) $ in Millions	Jun. 30, 2016	Dec. 31, 2015
Down Scenario [Member] | Mortgage Servicing Rights [Member]
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]
Net fair value 100 basis points	$ (531)	$ (598)
Net fair value 50 basis points	(284)	(250)
Net fair value 25 basis points	(147)	(114)
Down Scenario [Member] | Derivative [Member]
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]
Net fair value 100 basis points	541	475
Net fair value 50 basis points	282	226
Net fair value 25 basis points	143	107
Down Scenario [Member] | Net sensitivity [Member]
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]
Net fair value 100 basis points	10	(123)
Net fair value 50 basis points	(2)	(24)
Net fair value 25 basis points	(4)	(7)
Up Scenario [Member] | Mortgage Servicing Rights [Member]
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]
Net fair value 100 basis points	526	344
Net fair value 50 basis points	272	176
Net fair value 25 basis points	142	96
Up Scenario [Member] | Derivative [Member]
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]
Net fair value 100 basis points	(521)	(377)
Net fair value 50 basis points	(271)	(192)
Net fair value 25 basis points	(140)	(98)
Up Scenario [Member] | Net sensitivity [Member]
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]
Net fair value 100 basis points	5	(33)
Net fair value 50 basis points	1	(16)
Net fair value 25 basis points	$ 2	$ (2)