Mortgage Servicing Rights - Sensitivity to Changes in Interest Rates of the Fair Value of MSRs Portfolio and Related Derivative Instruments (Detail) - USD ($) $ in Millions	Mar. 31, 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	$ (590)	$ (598)
Net fair value 50 basis points	(296)	(250)
Net fair value 25 basis points	(145)	(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	528	475
Net fair value 50 basis points	274	226
Net fair value 25 basis points	138	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	(62)	(123)
Net fair value 50 basis points	(22)	(24)
Net fair value 25 basis points	(7)	(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	467	344
Net fair value 50 basis points	249	176
Net fair value 25 basis points	134	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	(517)	(377)
Net fair value 50 basis points	(263)	(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	(50)	(33)
Net fair value 50 basis points	$ (14)	(16)
Net fair value 25 basis points		$ (2)