Mortgage Servicing Rights - Sensitivity to Changes in Interest Rates of the Fair Value of MSRs Portfolio and Related Derivative Instruments (Detail) - USD ($) $ in Millions	Sep. 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	$ (576)	$ (598)
Net fair value 50 basis points	(291)	(250)
Net fair value 25 basis points	(148)	(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	542	475
Net fair value 50 basis points	281	226
Net fair value 25 basis points	140	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	(34)	(123)
Net fair value 50 basis points	(10)	(24)
Net fair value 25 basis points	(8)	(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	495	344
Net fair value 50 basis points	259	176
Net fair value 25 basis points	137	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	(523)	(377)
Net fair value 50 basis points	(264)	(192)
Net fair value 25 basis points	(134)	(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	(28)	(33)
Net fair value 50 basis points	(5)	(16)
Net fair value 25 basis points	$ 3	$ (2)