Mortgage Servicing Rights - Sensitivity to Changes in Interest Rates of the Fair Value of MSR Portfolio and Related Derivative Instruments (Detail) - USD ($) $ in Millions	Sep. 30, 2023	Dec. 31, 2022
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	$ (264)	$ (334)
Net fair value 50 basis points	(120)	(153)
Net fair value 25 basis points	(57)	(73)
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	262	337
Net fair value 50 basis points	117	153
Net fair value 25 basis points	55	73
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	(2)	3
Net fair value 50 basis points	(3)
Net fair value 25 basis points	(2)
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	172	224
Net fair value 50 basis points	96	125
Net fair value 25 basis points	51	66
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	(169)	(236)
Net fair value 50 basis points	(93)	(127)
Net fair value 25 basis points	(49)	(67)
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	3	(12)
Net fair value 50 basis points	3	(2)
Net fair value 25 basis points	$ 2	$ (1)