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
		Mar. 31, 2022	Mar. 31, 2021
Accumulated Other Comprehensive Income (Loss) [Line Items]
Balance at beginning of period		$ (1,943)	$ 322
Changes in unrealized gains (losses)		(6,754)	(3,378)
Changes in unrealized gains (losses)			99
Changes in unrealized gains (losses)		(6,754)	(3,279)
Foreign currency translation adjustment	[1]		25
Reclassification to earnings of realized (gains) losses		67	18
Applicable income taxes		1,692	819
Balance at end of period		(6,938)	(2,095)
Foreign Currency Translation [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Balance at beginning of period		(37)	(64)
Foreign currency translation adjustment	[1]		25
Applicable income taxes			(6)
Balance at end of period		(37)	(45)
Unrealized Gains (Losses) on Retirement Plans [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Balance at beginning of period		(1,426)	(1,842)
Reclassification to earnings of realized (gains) losses		32	39
Applicable income taxes		(8)	(10)
Balance at end of period		(1,402)	(1,813)
Unrealized Gains (Losses) on Derivative Hedges [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Balance at beginning of period		(85)	(189)
Changes in unrealized gains (losses)			99
Reclassification to earnings of realized (gains) losses		11	4
Applicable income taxes		(3)	(26)
Balance at end of period		(77)	(112)
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		(935)
Reclassification to earnings of realized (gains) losses		42
Applicable income taxes		(11)
Balance at end of period		(904)
Unrealized Gains (Losses) on Investment Securities Available-For-Sale [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Balance at beginning of period		540	2,417
Changes in unrealized gains (losses)		(6,754)	(3,378)
Reclassification to earnings of realized (gains) losses		(18)	(25)
Applicable income taxes		1,714	861
Balance at end of period		$ (4,518)	$ (125)

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