Investment Securities - Available-for-Sale and Held-to-Maturity (Detail) - USD ($) $ in Millions		Sep. 30, 2023		Dec. 31, 2022
Debt Securities Available For Sale And Held To Maturity [Line Items]
Held-to-maturity securities, Amortized Cost		$ 85,342	[1]	$ 88,740
Held-to-maturity securities, Unrealized Gains				3
Held-to-maturity securities, Unrealized Losses		(14,983)		(10,869)
Held-to-maturity securities, Fair Value		70,359	[1]	77,874
Available-for-sale Securities, Amortized Cost		76,755		81,450
Available-for-sale securities, Unrealized Gains		20		26
Available-for-sale securities, Unrealized Losses		(9,568)		(8,566)
Available-for-sale securities, Fair Value	[3]	67,207	[1],[2]	72,910
U.S. Treasury and Agencies [Member]
Debt Securities Available For Sale And Held To Maturity [Line Items]
Held-to-maturity securities, Amortized Cost		1,345		1,344
Held-to-maturity securities, Unrealized Losses		(62)		(51)
Held-to-maturity securities, Fair Value		1,283		1,293
Available-for-sale Securities, Amortized Cost		21,286		24,801
Available-for-sale securities, Unrealized Gains				1
Available-for-sale securities, Unrealized Losses		(2,579)		(2,769)
Available-for-sale securities, Fair Value		18,707		22,033
Residential Mortgage-Backed Securities [Member] | Agency [Member]
Debt Securities Available For Sale And Held To Maturity [Line Items]
Held-to-maturity securities, Amortized Cost		82,297		85,693
Held-to-maturity securities, Unrealized Gains				2
Held-to-maturity securities, Unrealized Losses		(14,851)		(10,810)
Held-to-maturity securities, Fair Value		67,446		74,885
Available-for-sale Securities, Amortized Cost		28,891		32,060
Available-for-sale securities, Unrealized Gains		2		8
Available-for-sale securities, Unrealized Losses		(3,279)		(2,797)
Available-for-sale securities, Fair Value		25,614		29,271
Commercial [Member] | Agency [Member]
Debt Securities Available For Sale And Held To Maturity [Line Items]
Held-to-maturity securities, Amortized Cost		1,700		1,703
Held-to-maturity securities, Unrealized Gains				1
Held-to-maturity securities, Unrealized Losses		(70)		(8)
Held-to-maturity securities, Fair Value		1,630		1,696
Available-for-sale Securities, Amortized Cost		8,711		8,736
Available-for-sale securities, Unrealized Losses		(1,769)		(1,591)
Available-for-sale securities, Fair Value		6,942		7,145
Commercial [Member] | Non Agency Securities [Member]
Debt Securities Available For Sale And Held To Maturity [Line Items]
Available-for-sale Securities, Amortized Cost		7		7
Available-for-sale securities, Unrealized Losses		(1)
Available-for-sale securities, Fair Value		6		7
Asset-Backed Securities [Member]
Debt Securities Available For Sale And Held To Maturity [Line Items]
Available-for-sale Securities, Amortized Cost		6,923	[4]	4,356
Available-for-sale securities, Unrealized Gains		8		5
Available-for-sale securities, Unrealized Losses		(63)		(38)
Available-for-sale securities, Fair Value		6,868	[4]	4,323
Obligations of State and Political Subdivisions [Member]
Debt Securities Available For Sale And Held To Maturity [Line Items]
Available-for-sale Securities, Amortized Cost		11,028	[5],[6]	11,484
Available-for-sale securities, Unrealized Gains		10		12
Available-for-sale securities, Unrealized Losses		(1,972)		(1,371)
Available-for-sale securities, Fair Value		9,066	[5],[6]	10,125
Other [Member]
Debt Securities Available For Sale And Held To Maturity [Line Items]
Available-for-sale Securities, Amortized Cost		4		6
Available-for-sale securities, Fair Value		4		6
Excluding Portfolio Level Basis Adjustments [Member]
Debt Securities Available For Sale And Held To Maturity [Line Items]
Available-for-sale Securities, Amortized Cost		76,850	[1],[2]	81,450
Available-for-sale securities, Unrealized Gains		20		26
Available-for-sale securities, Unrealized Losses		(9,663)		(8,566)
Available-for-sale securities, Fair Value		67,207		$ 72,910
Portfolio Level Basis Adjustments [Member]
Debt Securities Available For Sale And Held To Maturity [Line Items]
Available-for-sale Securities, Amortized Cost	[7]	(95)
Available-for-sale securities, Unrealized Losses	[7]	$ 95

[1] 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.

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

[3] Includes only collateral pledged by the Company where counterparties have the right to sell or pledge the collateral.

[4] Information related to asset and mortgage-backed securities included above is presented based upon weighted-average maturities that take into account anticipated future prepayments.

[5] Information related to obligations of state and political subdivisions is presented based upon yield to first optional call date if the security is purchased at a premium, and yield to maturity if the security is purchased at par or a discount.

[6] Maturity calculations for obligations of state and political subdivisions are based on the first optional call date for securities with a fair value above par and the contractual maturity date for securities with a fair value equal to or below par.

[7] 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.