Investment Securities - Amortized Cost, Fair Value and Yield by Maturity Date (Detail) - USD ($) $ in Millions		9 Months Ended		12 Months Ended
		Sep. 30, 2023		Dec. 31, 2022
Contractual Maturities of Investment Securities [Line Items]
Available-for-sale securities, Amortized Cost		$ 76,755		$ 81,450
Available-for-sale securities, total, fair value	[2]	$ 67,207	[1],[3]	$ 72,910
Available-for-sale securities, total, weighted-average maturity in years		7 years 3 months 18 days	[1],[3]	7 years 4 months 24 days
Available-for-sale securities, total, weighted-average yield		3.26%	[1],[3],[4]	2.94%
Held-to-maturity securities, Amortized Cost		$ 85,342	[3]	$ 88,740
Held-to-maturity securities, total, fair value		$ 70,359	[3]	$ 77,874
Held-to-maturity securities, total, weighted-average maturity in years		9 years 4 months 24 days	[3]	9 years 2 months 12 days
Held-to-maturity securities, total, weighted-average yield		2.20%	[3],[4]	2.18%
U.S. Treasury and Agencies [Member]
Contractual Maturities of Investment Securities [Line Items]
Available-for-sale securities, maturing in one year or less, amortized cost		$ 9
Available-for-sale securities, maturing after one year through five years, amortized cost		6,376
Available-for-sale securities, maturing after five years through ten years, amortized cost		13,089
Available-for-sale securities, maturing after ten years, amortized cost		1,812
Available-for-sale securities, Amortized Cost		21,286		$ 24,801
Available-for-sale securities, maturing in one year or less, fair value		9
Available-for-sale securities, maturing after one year through five years, fair value		6,049
Available-for-sale securities, maturing after five years through ten years, fair value		11,361
Available-for-sale securities, maturing after ten years, fair value		1,288
Available-for-sale securities, total, fair value		$ 18,707		22,033
Available-for-sale securities, maturing in one year or less, weighted-average maturity in years		2 months 12 days
Available-for-sale securities, maturing after one year through five years, weighted-average maturity in years		3 years 4 months 24 days
Available-for-sale securities, maturing after five years through ten years, weighted-average maturity in years		6 years 8 months 12 days
Available-for-sale securities, maturing after ten years, weighted- average maturity in years		11 years
Available-for-sale securities, total, weighted-average maturity in years		6 years 1 month 6 days
Available-for-sale securities, maturing in one year or less, weighted-average yield	[4]	5.24%
Available-for-sale securities, maturing after one year through five years, weighted-average yield	[4]	3.16%
Available-for-sale securities, maturing after five years through ten years, weighted-average yield	[4]	2.55%
Available-for-sale securities, maturing after ten years, weighted-average yield	[4]	2.02%
Available-for-sale securities, total, weighted-average yield	[4]	2.69%
Held-to-maturity securities, maturing in one year or less, amortized cost		$ 50
Held-to-maturity securities, maturing after one year through five years, amortized cost		1,295
Held-to-maturity securities, Amortized Cost		1,345		1,344
Held-to-maturity securities, maturing in one year or less, fair value		49
Held-to-maturity securities, maturing after one year through five years, fair value		1,234
Held-to-maturity securities, total, fair value		$ 1,283		1,293
Held-to-maturity securities, maturing in one year or less, weighted-average maturity in years		7 months 6 days
Held-to-maturity securities, maturing after one year through five years, weighted-average maturity in years		2 years 7 months 6 days
Held-to-maturity securities, total, weighted-average maturity in years		2 years 6 months
Held-to-maturity securities, maturing in one year or less, weighted-average yield	[4]	2.67%
Held-to-maturity securities, maturing after one year through five years, weighted-average yield	[4]	2.85%
Held-to-maturity securities, total, weighted-average yield	[4]	2.85%
Mortgage-Backed Securities [Member]
Contractual Maturities of Investment Securities [Line Items]
Available-for-sale securities, maturing in one year or less, amortized cost	[5]	$ 135
Available-for-sale securities, maturing after one year through five years, amortized cost	[5]	8,571
Available-for-sale securities, maturing after five years through ten years, amortized cost	[5]	27,049
Available-for-sale securities, maturing after ten years, amortized cost	[5]	1,854
Available-for-sale securities, Amortized Cost	[5]	37,609
Available-for-sale securities, maturing in one year or less, fair value	[5]	131
Available-for-sale securities, maturing after one year through five years, fair value	[5]	7,846
Available-for-sale securities, maturing after five years through ten years, fair value	[5]	23,053
Available-for-sale securities, maturing after ten years, fair value	[5]	1,532
Available-for-sale securities, total, fair value	[5]	$ 32,562
Available-for-sale securities, maturing in one year or less, weighted-average maturity in years	[5]	9 months 18 days
Available-for-sale securities, maturing after one year through five years, weighted-average maturity in years	[5]	3 years 1 month 6 days
Available-for-sale securities, maturing after five years through ten years, weighted-average maturity in years	[5]	7 years 7 months 6 days
Available-for-sale securities, maturing after ten years, weighted- average maturity in years	[5]	10 years 10 months 24 days
Available-for-sale securities, total, weighted-average maturity in years	[5]	6 years 8 months 12 days
Available-for-sale securities, maturing in one year or less, weighted-average yield	[4],[5]	2.52%
Available-for-sale securities, maturing after one year through five years, weighted-average yield	[4],[5]	2.45%
Available-for-sale securities, maturing after five years through ten years, weighted-average yield	[4],[5]	3.24%
Available-for-sale securities, maturing after ten years, weighted-average yield	[4],[5]	3.49%
Available-for-sale securities, total, weighted-average yield	[4],[5]	3.07%
Held-to-maturity securities, maturing in one year or less, amortized cost	[5]	$ 20
Held-to-maturity securities, maturing after one year through five years, amortized cost	[5]	1,347
Held-to-maturity securities, maturing after five years through ten years, amortized cost	[5]	57,099
Held-to-maturity securities, maturing after ten years, amortized cost	[5]	25,531
Held-to-maturity securities, Amortized Cost	[5]	83,997
Held-to-maturity securities, maturing in one year or less, fair value	[5]	19
Held-to-maturity securities, maturing after one year through five years, fair value	[5]	1,318
Held-to-maturity securities, maturing after five years through ten years, fair value	[5]	47,115
Held-to-maturity securities, maturing after ten years, fair value	[5]	20,624
Held-to-maturity securities, total, fair value	[5]	$ 69,076
Held-to-maturity securities, maturing in one year or less, weighted-average maturity in years	[5]	8 months 12 days
Held-to-maturity securities, maturing after one year through five years, weighted-average maturity in years	[5]	2 years 7 months 6 days
Held-to-maturity securities, maturing after five years through ten years, weighted-average maturity in years	[5]	9 years 3 months 18 days
Held-to-maturity securities, maturing after ten years, weighted-average maturity in years	[5]	10 years 3 months 18 days
Held-to-maturity securities, total, weighted-average maturity in years	[5]	9 years 6 months
Held-to-maturity securities, maturing in one year or less, weighted-average yield	[4],[5]	4.67%
Held-to-maturity securities, maturing after one year through five years, weighted-average yield	[4],[5]	4.59%
Held-to-maturity securities, maturing after five years through ten years, weighted-average yield	[4],[5]	2.17%
Held-to-maturity securities, maturing after ten years, weighted-average yield	[4],[5]	2.12%
Held-to-maturity securities, total, weighted-average yield	[4],[5]	2.19%
Asset-Backed Securities [Member]
Contractual Maturities of Investment Securities [Line Items]
Available-for-sale securities, maturing in one year or less, amortized cost	[5]	$ 1,714
Available-for-sale securities, maturing after one year through five years, amortized cost	[5]	4,731
Available-for-sale securities, maturing after five years through ten years, amortized cost	[5]	478
Available-for-sale securities, Amortized Cost		6,923	[5]	4,356
Available-for-sale securities, maturing in one year or less, fair value	[5]	1,683
Available-for-sale securities, maturing after one year through five years, fair value	[5]	4,706
Available-for-sale securities, maturing after five years through ten years, fair value	[5]	479
Available-for-sale securities, total, fair value		$ 6,868	[5]	4,323
Available-for-sale securities, maturing in one year or less, weighted-average maturity in years	[5]	2 months 12 days
Available-for-sale securities, maturing after one year through five years, weighted-average maturity in years	[5]	1 year 8 months 12 days
Available-for-sale securities, maturing after five years through ten years, weighted-average maturity in years	[5]	5 years 6 months
Available-for-sale securities, total, weighted-average maturity in years	[5]	1 year 7 months 6 days
Available-for-sale securities, maturing in one year or less, weighted-average yield	[4],[5]	4.25%
Available-for-sale securities, maturing after one year through five years, weighted-average yield	[4],[5]	5.35%
Available-for-sale securities, maturing after five years through ten years, weighted-average yield	[4],[5]	7.07%
Available-for-sale securities, total, weighted-average yield	[4],[5]	5.20%
Obligations of State and Political Subdivisions [Member]
Contractual Maturities of Investment Securities [Line Items]
Available-for-sale securities, maturing in one year or less, amortized cost	[6],[7]	$ 36
Available-for-sale securities, maturing after one year through five years, amortized cost	[6],[7]	381
Available-for-sale securities, maturing after five years through ten years, amortized cost	[6],[7]	507
Available-for-sale securities, maturing after ten years, amortized cost	[6],[7]	10,104
Available-for-sale securities, Amortized Cost		11,028	[6],[7]	11,484
Available-for-sale securities, maturing in one year or less, fair value	[6],[7]	36
Available-for-sale securities, maturing after one year through five years, fair value	[6],[7]	378
Available-for-sale securities, maturing after five years through ten years, fair value	[6],[7]	472
Available-for-sale securities, maturing after ten years, fair value	[6],[7]	8,180
Available-for-sale securities, total, fair value		$ 9,066	[6],[7]	10,125
Available-for-sale securities, maturing in one year or less, weighted-average maturity in years	[6],[7]	7 months 6 days
Available-for-sale securities, maturing after one year through five years, weighted-average maturity in years	[6],[7]	3 years 3 months 18 days
Available-for-sale securities, maturing after five years through ten years, weighted-average maturity in years	[6],[7]	7 years 9 months 18 days
Available-for-sale securities, maturing after ten years, weighted- average maturity in years	[6],[7]	15 years 9 months 18 days
Available-for-sale securities, total, weighted-average maturity in years	[6],[7]	14 years 10 months 24 days
Available-for-sale securities, maturing in one year or less, weighted-average yield	[4],[6],[7]	7.96%
Available-for-sale securities, maturing after one year through five years, weighted-average yield	[4],[6],[7]	5.74%
Available-for-sale securities, maturing after five years through ten years, weighted-average yield	[4],[6],[7]	4.43%
Available-for-sale securities, maturing after ten years, weighted-average yield	[4],[6],[7]	3.65%
Available-for-sale securities, total, weighted-average yield	[4],[6],[7]	3.77%
Other [Member]
Contractual Maturities of Investment Securities [Line Items]
Available-for-sale securities, maturing after one year through five years, amortized cost		$ 4
Available-for-sale securities, Amortized Cost		4		6
Available-for-sale securities, maturing after one year through five years, fair value		4
Available-for-sale securities, total, fair value		$ 4		6
Available-for-sale securities, maturing after one year through five years, weighted-average maturity in years		1 year 8 months 12 days
Available-for-sale securities, total, weighted-average maturity in years		1 year 8 months 12 days
Available-for-sale securities, maturing after one year through five years, weighted-average yield	[4]	1.89%
Available-for-sale securities, total, weighted-average yield	[4]	1.89%
Excluding Portfolio Level Basis Adjustments [Member]
Contractual Maturities of Investment Securities [Line Items]
Available-for-sale securities, Amortized Cost		$ 76,850	[1],[3]	81,450
Available-for-sale securities, total, fair value		$ 67,207		$ 72,910

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

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

[3] 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.

[4] 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.

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

[6] 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.

[7] 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.