Accumulated Other Comprehensive Income (Loss) - Impact to Net Income for Items Reclassified out of Accumulated Other Comprehensive Income and into Earnings (Detail) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2023	Jun. 30, 2022	Jun. 30, 2023	Jun. 30, 2022
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Realized gains (losses) on sale of investment securities	$ 3	$ 19	$ (29)	$ 37
Amortization of unrealized gains (losses)	7,526	3,825	14,490	7,243
Realized gains (losses) on derivative hedges	(3,111)	(390)	(5,441)	(635)
Actuarial gains (losses) and prior service cost (credit) amortization	(353)	(340)	(778)	(662)
Applicable income taxes	(382)	(414)	(837)	(811)
Net income (loss)	1,369	1,534	3,073	3,092
Reclassification Out of Accumulated Other Comprehensive Income [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Net income (loss)	(111)	(63)	(229)	(113)
Reclassification Out of Accumulated Other Comprehensive Income [Member] | Unrealized Gains (Losses) on Investment Securities Available-For-Sale [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Realized gains (losses) on sale of investment securities	3	19	(29)	37
Applicable income taxes	(1)	(5)	7	(9)
Net income (loss)	2	14	(22)	28
Reclassification Out of Accumulated Other Comprehensive Income [Member] | Unrealized Gains (Losses) on Investment Securities Transferred From Available For Sale to Held To Maturity [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Amortization of unrealized gains (losses)	(141)	(61)	(262)	(103)
Applicable income taxes	35	16	66	26
Net income (loss)	(106)	(45)	(196)	(77)
Reclassification Out of Accumulated Other Comprehensive Income [Member] | Unrealized Gains (Losses) on Derivative Hedges [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Realized gains (losses) on derivative hedges	(11)	(10)	(18)	(21)
Applicable income taxes	3	2	4	5
Net income (loss)	(8)	(8)	(14)	(16)
Reclassification Out of Accumulated Other Comprehensive Income [Member] | Unrealized Gains (Losses) on Retirement Plans [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Actuarial gains (losses) and prior service cost (credit) amortization	2	(32)	4	(64)
Applicable income taxes	(1)	8	(1)	16
Net income (loss)	$ 1	$ (24)	$ 3	$ (48)