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			9 Months Ended
	Sep. 30, 2023	Sep. 30, 2022		Sep. 30, 2023	Sep. 30, 2022
Accumulated Other Comprehensive Income (Loss) [Line Items]
Balance at beginning of period	$ (10,718)	$ (10,361)		$ (11,407)	$ (1,943)
Changes in unrealized gains (losses)	(1,881)	(2,810)		(1,036)	(14,325)
Changes in unrealized gains (losses)	(349)	(232)		(610)	(134)
Changes in unrealized gains (losses)	(1)
Changes in unrealized gains (losses)	(2,231)	(3,042)		(1,646)	(14,459)
Foreign currency translation adjustment	3	(8)	[1]	21	(11)	[1]
Reclassification to earnings of realized (gains) losses	170	186		475	337
Applicable income taxes	521	725		302	3,576
Balance at end of period	(12,255)	(12,500)		(12,255)	(12,500)
Unrealized Gains (Losses) on Investment Securities Available-For-Sale [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Balance at beginning of period	(5,716)	(7,058)		(6,378)	540
Changes in unrealized gains (losses)	(1,881)	(2,810)		(1,036)	(14,325)
Transfer of securities from available-for-sale to held-to-maturity		3,032			4,413
Reclassification to earnings of realized (gains) losses		(1)		29	(38)
Applicable income taxes	474	(56)		262	2,517
Balance at end of period	(7,123)	(6,893)		(7,123)	(6,893)
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	(3,737)	(1,890)		(3,933)	(935)
Transfer of securities from available-for-sale to held-to-maturity		(3,032)			(4,413)
Reclassification to earnings of realized (gains) losses	144	147		406	250
Applicable income taxes	(37)	730		(103)	1,053
Balance at end of period	(3,630)	(4,045)		(3,630)	(4,045)
Unrealized Gains (Losses) on Derivative Hedges [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Balance at beginning of period	(294)	4		(114)	(85)
Changes in unrealized gains (losses)	(349)	(232)		(610)	(134)
Reclassification to earnings of realized (gains) losses	28	8		46	29
Applicable income taxes	82	57		145	27
Balance at end of period	(533)	(163)		(533)	(163)
Unrealized Gains (Losses) on Retirement Plans [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Balance at beginning of period	(941)	(1,378)		(939)	(1,426)
Changes in unrealized gains (losses)	(1)
Reclassification to earnings of realized (gains) losses	(2)	32		(6)	96
Applicable income taxes	2	(8)		3	(24)
Balance at end of period	(942)	(1,354)		(942)	(1,354)
Foreign Currency Translation [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Balance at beginning of period	(30)	(39)		(43)	(37)
Foreign currency translation adjustment	3	(8)	[1]	21	(11)	[1]
Applicable income taxes		2		(5)	3
Balance at end of period	$ (27)	$ (45)		$ (27)	$ (45)

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