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		9 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Realized gains (losses) on sale of investment securities	$ 0	$ 1	$ (29)	$ 38
Amortization of unrealized gains (losses)	7,754	4,728	22,244	11,971
Realized gains (losses) on derivative hedges	(3,518)	(901)	(8,959)	(1,536)
Actuarial gains (losses) and prior service cost (credit) amortization	(343)	(336)	(1,121)	(998)
Applicable income taxes	(431)	(481)	(1,268)	(1,292)
Net income (loss)	1,524	1,816	4,597	4,908
Reclassification Out of Accumulated Other Comprehensive Income [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Net income (loss)	(126)	(139)	(355)	(252)
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	0	1	(29)	38
Applicable income taxes	0	0	7	(9)
Net income (loss)	0	1	(22)	29
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)	(144)	(147)	(406)	(250)
Applicable income taxes	37	37	103	63
Net income (loss)	(107)	(110)	(303)	(187)
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	(28)	(8)	(46)	(29)
Applicable income taxes	8	2	12	7
Net income (loss)	(20)	(6)	(34)	(22)
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)	6	(96)
Applicable income taxes	(1)	8	(2)	24
Net income (loss)	$ 1	$ (24)	$ 4	$ (72)