Mortgage Servicing Rights - Sensitivity to Changes in Interest Rates of the Fair Value of MSR Portfolio and Related Derivative Instruments (Detail) - USD ($) $ in Millions	Jun. 30, 2020	Dec. 31, 2019
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	$ (323)	$ (663)
Net fair value 50 basis points	(216)	(316)
Net fair value 25 basis points	(124)	(153)
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	422	613
Net fair value 50 basis points	229	306
Net fair value 25 basis points	121	152
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	99	(50)
Net fair value 50 basis points	13	(10)
Net fair value 25 basis points	(3)	(1)
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	687	485
Net fair value 50 basis points	321	269
Net fair value 25 basis points	151	141
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	(611)	(550)
Net fair value 50 basis points	(285)	(279)
Net fair value 25 basis points	(136)	(143)
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	76	(65)
Net fair value 50 basis points	36	(10)
Net fair value 25 basis points	$ 15	$ (2)