Investment Securities - Amortized Cost, Fair Value and Yield by Maturity Date (Parenthetical) (Detail) - USD ($) $ in Millions		3 Months Ended			9 Months Ended			12 Months Ended
		Sep. 30, 2023		Sep. 30, 2022	Sep. 30, 2023		Sep. 30, 2022	Dec. 31, 2022
Contractual Maturities of Investment Securities [Line Items]
Federal statutory rate		21.00%		21.00%	21.00%		21.00%
Available for sale securities weighted average maturities					7 years 3 months 18 days	[1],[2]		7 years 4 months 24 days
Debt securities available for sale weighted average yield		3.26%	[1],[2],[3]		3.26%	[1],[2],[3]		2.94%
Debt Securities, Available-for-sale, Amortized Cost		$ 76,755			$ 76,755			$ 81,450
Weighted average maturity of total held to maturity investment securities					9 years 4 months 24 days	[2]		9 years 2 months 12 days
Debt Securities, Held-to-Maturity, Weighted Average Yield		2.20%	[2],[3]		2.20%	[2],[3]		2.18%
Portfolio Level Basis Adjustments [Member]
Contractual Maturities of Investment Securities [Line Items]
Debt Securities, Available-for-sale, Amortized Cost	[4]	$ (95)			$ (95)

[1] Amortized cost excludes portfolio level basis adjustments of $(95) million.

[2] The weighted-average maturity of total held-to-maturity investment securities was 9.2 years at December 31, 2022, with a corresponding weighted-average yield of 2.18 percent. The weighted-average maturity of total available-for-sale investment securities was 7.4 years at December 31, 2022, with a corresponding weighted-average yield of 2.94 percent.

[3] Weighted-average yields for obligations of state and political subdivisions are presented on a fully-taxable equivalent basis based on a federal income tax rate of 21 percent. Yields on investment securities are computed based on amortized cost balances, excluding any premiums or discounts recorded related to the transfer of investment securities at fair value from available-for-sale to held-to-maturity.

[4] Represents fair value hedge basis adjustments related to active portfolio layer method hedges of available-for-sale investment securities, which are not allocated to individual securities in the portfolio. For additional information, refer to note 13.