Accumulated Other Comprehensive Income (Loss) - Reconciliation of Transactions Affecting Accumulated Other Comprehensive Income (Loss) Included in Shareholders' Equity (Detail) - USD ($) $ in Millions		3 Months Ended		6 Months Ended
		Jun. 30, 2023	Jun. 30, 2022	Jun. 30, 2023	Jun. 30, 2022
Accumulated Other Comprehensive Income (Loss) [Line Items]
Balance at beginning of period		$ (10,153)	$ (6,938)	$ (11,407)	$ (1,943)
Changes in unrealized gains (losses)		(460)	(4,761)	845	(11,515)
Changes in unrealized gains (losses)		(465)	98	(261)	98
Changes in unrealized gains (losses)				1
Changes in unrealized gains (losses)		(925)	(4,663)	585	(11,417)
Foreign currency translation adjustment	[1]	19	(3)	18	(3)
Reclassification to earnings of realized (gains) losses		147	84	305	151
Applicable income taxes		194	1,159	(219)	2,851
Balance at end of period		(10,718)	(10,361)	(10,718)	(10,361)
Unrealized Gains (Losses) on Investment Securities Available-For-Sale [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Balance at beginning of period		(5,369)	(4,518)	(6,378)	540
Changes in unrealized gains (losses)		(460)	(4,761)	845	(11,515)
Transfer of securities from available-for-sale to held-to-maturity			1,381		1,381
Reclassification to earnings of realized (gains) losses		(3)	(19)	29	(37)
Applicable income taxes		116	859	(212)	2,573
Balance at end of period		(5,716)	(7,058)	(5,716)	(7,058)
Unrealized Gains (Losses) on Investment Securities Transferred From Available For Sale to Held To Maturity [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Balance at beginning of period		(3,843)	(904)	(3,933)	(935)
Transfer of securities from available-for-sale to held-to-maturity			(1,381)		(1,381)
Reclassification to earnings of realized (gains) losses		141	61	262	103
Applicable income taxes		(35)	334	(66)	323
Balance at end of period		(3,737)	(1,890)	(3,737)	(1,890)
Unrealized Gains (Losses) on Derivative Hedges [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Balance at beginning of period		43	(77)	(114)	(85)
Changes in unrealized gains (losses)		(465)	98	(261)	98
Reclassification to earnings of realized (gains) losses		11	10	18	21
Applicable income taxes		117	(27)	63	(30)
Balance at end of period		(294)	4	(294)	4
Unrealized Gains (Losses) on Retirement Plans [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Balance at beginning of period		(940)	(1,402)	(939)	(1,426)
Changes in unrealized gains (losses)				1
Reclassification to earnings of realized (gains) losses		(2)	32	(4)	64
Applicable income taxes		1	(8)	1	(16)
Balance at end of period		(941)	(1,378)	(941)	(1,378)
Foreign Currency Translation [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Balance at beginning of period		(44)	(37)	(43)	(37)
Foreign currency translation adjustment	[1]	19	(3)	18	(3)
Applicable income taxes		(5)	1	(5)	1
Balance at end of period		$ (30)	$ (39)	$ (30)	$ (39)

[1] Represents the impact of changes in foreign currency exchange rates on the Company’s investment in foreign operations and related hedges.