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, 2022	Sep. 30, 2021	Sep. 30, 2022	Sep. 30, 2021
Accumulated Other Comprehensive Income (Loss) [Line Items]
Balance at beginning of period		$ (10,361)	$ (1,202)	$ (1,943)	$ 322
Changes in unrealized gains (losses)		(2,810)	(825)	(14,325)	(3,008)
Changes in unrealized gains (losses)		(232)	8	(134)	121
Changes in unrealized gains (losses)		(3,042)	(817)	(14,459)	(2,887)
Foreign currency translation adjustment	[1]	(8)	(1)	(11)	23
Reclassification to earnings of realized (gains) losses		186	27	337	34
Applicable income taxes		725	201	3,576	716
Balance at end of period		(12,500)	(1,792)	(12,500)	(1,792)
Foreign Currency Translation [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Balance at beginning of period		(39)	(47)	(37)	(64)
Foreign currency translation adjustment	[1]	(8)	(1)	(11)	23
Applicable income taxes		2		3	(7)
Balance at end of period		(45)	(48)	(45)	(48)
Unrealized Gains (Losses) on Retirement Plans [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Balance at beginning of period		(1,378)	(1,783)	(1,426)	(1,842)
Reclassification to earnings of realized (gains) losses		32	39	96	118
Applicable income taxes		(8)	(10)	(24)	(30)
Balance at end of period		(1,354)	(1,754)	(1,354)	(1,754)
Unrealized Gains (Losses) on Derivative Hedges [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Balance at beginning of period		4	(107)	(85)	(189)
Changes in unrealized gains (losses)		(232)	8	(134)	121
Reclassification to earnings of realized (gains) losses		8	8	29	4
Applicable income taxes		57	(4)	27	(31)
Balance at end of period		(163)	(95)	(163)	(95)
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		(1,890)		(935)
Transfer of securities from available-for-sale to held-to-maturity		(3,032)		(4,413)
Reclassification to earnings of realized (gains) losses		147		250
Applicable income taxes		730		1,053
Balance at end of period		(4,045)		(4,045)
Unrealized Gains (Losses) on Investment Securities Available-For-Sale [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Balance at beginning of period		(7,058)	735	540	2,417
Changes in unrealized gains (losses)		(2,810)	(825)	(14,325)	(3,008)
Transfer of securities from available-for-sale to held-to-maturity		3,032		4,413
Reclassification to earnings of realized (gains) losses		(1)	(20)	(38)	(88)
Applicable income taxes		(56)	215	2,517	784
Balance at end of period		$ (6,893)	$ 105	$ (6,893)	$ 105

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