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, 2022	Jun. 30, 2021	Jun. 30, 2022	Jun. 30, 2021
Accumulated Other Comprehensive Income (Loss) [Line Items]
Balance at beginning of period		$ (6,938)	$ (2,095)	$ (1,943)	$ 322
Changes in unrealized gains (losses)		(4,761)	1,195	(11,515)	(2,183)
Changes in unrealized gains (losses)		98	14	98	113
Changes in unrealized gains (losses)		(4,663)	1,209	(11,417)	(2,070)
Foreign currency translation adjustment	[1]	(3)	(1)	(3)	24
Reclassification to earnings of realized (gains) losses		84	(11)	151	7
Applicable income taxes		1,159	(304)	2,851	515
Balance at end of period		(10,361)	(1,202)	(10,361)	(1,202)
Foreign Currency Translation [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Balance at beginning of period		(37)	(45)	(37)	(64)
Foreign currency translation adjustment	[1]	(3)	(1)	(3)	24
Applicable income taxes		1	(1)	1	(7)
Balance at end of period		(39)	(47)	(39)	(47)
Unrealized Gains (Losses) on Retirement Plans [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Balance at beginning of period		(1,402)	(1,813)	(1,426)	(1,842)
Foreign currency translation adjustment	[1]	0		0
Reclassification to earnings of realized (gains) losses		32	40	64	79
Applicable income taxes		(8)	(10)	(16)	(20)
Balance at end of period		(1,378)	(1,783)	(1,378)	(1,783)
Unrealized Gains (Losses) on Derivative Hedges [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Balance at beginning of period		(77)	(112)	(85)	(189)
Changes in unrealized gains (losses)		98	14	98	113
Foreign currency translation adjustment	[1]	0		0
Reclassification to earnings of realized (gains) losses		10	(8)	21	(4)
Applicable income taxes		(27)	(1)	(30)	(27)
Balance at end of period		4	(107)	4	(107)
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		(904)		(935)
Changes in unrealized gains (losses)		0		0
Transfer of securities from available-for-sale to held-to-maturity		(1,381)		(1,381)
Foreign currency translation adjustment	[1]	0		0
Reclassification to earnings of realized (gains) losses		61		103
Applicable income taxes		334		323
Balance at end of period		(1,890)		(1,890)
Unrealized Gains (Losses) on Investment Securities Available-For-Sale [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Balance at beginning of period		(4,518)	(125)	540	2,417
Changes in unrealized gains (losses)		(4,761)	1,195	(11,515)	(2,183)
Transfer of securities from available-for-sale to held-to-maturity		1,381		1,381
Foreign currency translation adjustment	[1]	0		0
Reclassification to earnings of realized (gains) losses		(19)	(43)	(37)	(68)
Applicable income taxes		859	(292)	2,573	569
Balance at end of period		$ (7,058)	$ 735	$ (7,058)	$ 735

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