Fair Values of Assets and Liabilities - Changes in Fair Value for All Assets and Liabilities Measured at Fair Value on Recurring Basis Using Significant Unobservable Inputs (Level 3) (Detail) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2023	Mar. 31, 2022
Mortgage Servicing Rights [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Beginning of Period Balance	$ 3,755	$ 2,953
Net Gains (Losses) Included in Net Income	(129)	238
Purchases	1	3
Sales	1	1
Issuances	96	237
Settlements	0	0
End of Period Balance	3,724	3,432
Net Change in Unrealized Gains (Losses) Relating to Assets and Liabilities Held at End of Period	$ (129)	$ 238
Fair Value, Asset, Recurring Basis, Unobservable Input Reconciliation, Gain (Loss), Statement of Income or Comprehensive Income [Extensible Enumeration]	Net Income (Loss), Including Portion Attributable to Noncontrolling Interest	Net Income (Loss), Including Portion Attributable to Noncontrolling Interest
Available-for-Sale Securities [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Beginning of Period Balance	$ 1	$ 8
Net Gains (Losses) Included in Net Income	$ 0	$ 0
Fair Value, Asset, Recurring Basis, Unobservable Input Reconciliation, Asset, Gain (Loss), Statement of Other Comprehensive Income or Comprehensive Income [Extensible Enumeration]	Other Comprehensive Income (Loss), Securities, Available-for-Sale, Unrealized Holding Gain (Loss) Arising During Period, before Tax	Other Comprehensive Income (Loss), Securities, Available-for-Sale, Unrealized Holding Gain (Loss) Arising During Period, before Tax
Purchases	$ 0	$ 0
Sales	0	0
Issuances	0	0
Settlements	0	0
End of Period Balance	1	8
Net Change in Unrealized Gains (Losses) Relating to Assets and Liabilities Held at End of Period	$ 0	$ 0
Fair Value, Asset, Recurring Basis, Still Held, Unrealized Gain (Loss), Statement of Income or Comprehensive Income [Extensible Enumeration]	Net Change in Unrealized Gains (Losses) Relating to Assets and Liabilities Held at End of Period	Net Change in Unrealized Gains (Losses) Relating to Assets and Liabilities Held at End of Period
Available-for-Sale Securities [Member] | Obligations of State and Political Subdivisions [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Beginning of Period Balance	$ 1	$ 1
Net Gains (Losses) Included in Net Income	0	0
Purchases	0	0
Sales	0	0
Issuances	0	0
Settlements	0	0
End of Period Balance	1	1
Net Change in Unrealized Gains (Losses) Relating to Assets and Liabilities Held at End of Period	$ 0	$ 0
Fair Value, Asset, Recurring Basis, Still Held, Unrealized Gain (Loss), Statement of Income or Comprehensive Income [Extensible Enumeration]	Net Change in Unrealized Gains (Losses) Relating to Assets and Liabilities Held at End of Period	Net Change in Unrealized Gains (Losses) Relating to Assets and Liabilities Held at End of Period
Derivative [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Beginning of Period Balance	$ (3,199)	$ 799
Net Gains (Losses) Included in Net Income	(316)	(1,867)
Purchases	423	11
Sales	(12)	(1)
Issuances	0	0
Settlements	839	47
End of Period Balance	(2,265)	(1,011)
Net Change in Unrealized Gains (Losses) Relating to Assets and Liabilities Held at End of Period	$ 529	$ (1,697)
Fair Value, Net Derivative Asset (Liability), Recurring Basis, Unobservable Input Reconciliation, Gain (Loss), Statement of Income or Comprehensive Income [Extensible Enumeration]	Net Gains (Losses) Included in Net Income	Net Gains (Losses) Included in Net Income
Asset-Backed Securities [Member] | Available-for-Sale Securities [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Beginning of Period Balance		$ 7
Net Gains (Losses) Included in Net Income		0
Purchases		0
Sales		0
Issuances		0
Settlements		0
End of Period Balance		7
Net Change in Unrealized Gains (Losses) Relating to Assets and Liabilities Held at End of Period		$ 0
Fair Value, Asset, Recurring Basis, Still Held, Unrealized Gain (Loss), Statement of Income or Comprehensive Income [Extensible Enumeration]		Net Change in Unrealized Gains (Losses) Relating to Assets and Liabilities Held at End of Period