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		6 Months Ended
	Jun. 30, 2023	Jun. 30, 2022	Jun. 30, 2023	Jun. 30, 2022
Mortgage Servicing Rights [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Beginning of Period Balance	$ 3,724	$ 3,432	$ 3,755	$ 2,953
Net Gains (Losses) Included in Net Income	(42)	170	(171)	408
Purchases	1	3	2	6
Sales	(149)	0	(148)	1
Principal Payments	0	0	0	0
Issuances	99	102	195	339
Settlements	0	0	0	0
End of Period Balance	3,633	3,707	3,633	3,707
Net Change in Unrealized Gains (Losses) Relating to Assets and Liabilities Held at End of Period	(42)	170	(171)	408
Available-for-Sale Securities [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Beginning of Period Balance	1	8	1	8
Net Gains (Losses) Included in Net Income	0	(3)	0	(3)
Purchases	0	0	0	0
Sales	0	(4)	0	(4)
Principal Payments	(1)	0	(1)	0
Issuances	0	0	0	0
Settlements	0	0	0	0
End of Period Balance	0	1	0	1
Net Change in Unrealized Gains (Losses) Relating to Assets and Liabilities Held at End of Period	0	0	0	0
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	1	1
Net Gains (Losses) Included in Net Income	0	0	0	0
Purchases	0	0	0	0
Sales	0	0	0	0
Principal Payments	(1)	0	(1)	0
Issuances	0	0	0	0
Settlements	0	0	0	0
End of Period Balance	0	1	0	1
Net Change in Unrealized Gains (Losses) Relating to Assets and Liabilities Held at End of Period	0	0	0	0
Derivative [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Beginning of Period Balance	(2,265)	(1,011)	(3,199)	799
Net Gains (Losses) Included in Net Income	(1,927)	(1,494)	(2,243)	(3,361)
Purchases	(18)	81	405	92
Sales	(7)	0	(19)	(1)
Principal Payments	0	0	0	0
Issuances	0	0	0	0
Settlements	798	249	1,637	296
End of Period Balance	(3,419)	(2,175)	(3,419)	(2,175)
Net Change in Unrealized Gains (Losses) Relating to Assets and Liabilities Held at End of Period	$ (1,631)	(1,259)	$ (1,242)	(2,739)
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		7
Net Gains (Losses) Included in Net Income		(3)		(3)
Purchases		0		0
Sales		(4)		(4)
Principal Payments		0		0
Issuances		0		0
Settlements		0		0
End of Period Balance		0		0
Net Change in Unrealized Gains (Losses) Relating to Assets and Liabilities Held at End of Period		$ 0		$ 0