Investment Securities - Amortized Cost, Fair Value and Yield by Maturity Date (Detail) - USD ($) $ in Millions		3 Months Ended		12 Months Ended
		Mar. 31, 2022		Dec. 31, 2021
Contractual Maturities of Investment Securities [Line Items]
Available-for-sale securities, Amortized Cost		$ 129,642	[1]	$ 132,241
Available-for-sale securities, total, fair value		$ 123,593	[1]	$ 132,963
Available-for-sale securities, total, weighted-average maturity in years		7 years 6 months	[1]	7 years 4 months 24 days
Available-for-sale securities, total, weighted-average yield		1.96%	[1],[2]	1.45%
Held-to-maturity securities, Amortized Cost		$ 43,654	[1]	$ 41,858
Held-to-maturity securities, total, fair value		$ 40,572	[1]	$ 41,812
Held-to-maturity securities, total, weighted-average maturity in years	[1]	9 years 8 months 12 days
Held-to-maturity securities, total, weighted-average yield		1.64%	[1],[2]	1.73%
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		$ 2,226
Available-for-sale securities, maturing after one year through five years, amortized cost		3,246
Available-for-sale securities, maturing after five years through ten years, amortized cost		19,476
Available-for-sale securities, maturing after ten years, amortized cost		2,705
Available-for-sale securities, Amortized Cost		27,653		$ 36,648
Available-for-sale securities, maturing in one year or less, fair value		2,236
Available-for-sale securities, maturing after one year through five years, fair value		3,086
Available-for-sale securities, maturing after five years through ten years, fair value		18,644
Available-for-sale securities, maturing after ten years, fair value		2,384
Available-for-sale securities, total, fair value		$ 26,350		36,609
Available-for-sale securities, maturing in one year or less, weighted-average maturity in years		6 months
Available-for-sale securities, maturing after one year through five years, weighted-average maturity in years		4 years 8 months 12 days
Available-for-sale securities, maturing after five years through ten years, weighted-average maturity in years		7 years 8 months 12 days
Available-for-sale securities, maturing after ten years, weighted- average maturity in years		12 years
Available-for-sale securities, total, weighted-average maturity in years		7 years 2 months 12 days
Available-for-sale securities, maturing in one year or less, weighted-average yield	[2]	1.97%
Available-for-sale securities, maturing after one year through five years, weighted-average yield	[2]	1.36%
Available-for-sale securities, maturing after five years through ten years, weighted-average yield	[2]	1.88%
Available-for-sale securities, maturing after ten years, weighted-average yield	[2]	1.99%
Available-for-sale securities, total, weighted-average yield	[2]	1.83%
Mortgage-Backed Securities [Member]
Contractual Maturities of Investment Securities [Line Items]
Available-for-sale securities, maturing in one year or less, amortized cost	[3]	$ 64
Available-for-sale securities, maturing after one year through five years, amortized cost	[3]	15,629
Available-for-sale securities, maturing after five years through ten years, amortized cost	[3]	69,960
Available-for-sale securities, maturing after ten years, amortized cost	[3]	5,624
Available-for-sale securities, Amortized Cost	[3]	91,277
Available-for-sale securities, maturing in one year or less, fair value	[3]	65
Available-for-sale securities, maturing after one year through five years, fair value	[3]	15,395
Available-for-sale securities, maturing after five years through ten years, fair value	[3]	66,155
Available-for-sale securities, maturing after ten years, fair value	[3]	5,340
Available-for-sale securities, total, fair value	[3]	$ 86,955
Available-for-sale securities, maturing in one year or less, weighted-average maturity in years	[3]	8 months 12 days
Available-for-sale securities, maturing after one year through five years, weighted-average maturity in years	[3]	3 years 3 months 18 days
Available-for-sale securities, maturing after five years through ten years, weighted-average maturity in years	[3]	8 years
Available-for-sale securities, maturing after ten years, weighted- average maturity in years	[3]	10 years 4 months 24 days
Available-for-sale securities, total, weighted-average maturity in years	[3]	7 years 3 months 18 days
Available-for-sale securities, maturing in one year or less, weighted-average yield	[2],[3]	2.19%
Available-for-sale securities, maturing after one year through five years, weighted-average yield	[2],[3]	1.89%
Available-for-sale securities, maturing after five years through ten years, weighted-average yield	[2],[3]	1.76%
Available-for-sale securities, maturing after ten years, weighted-average yield	[2],[3]	2.09%
Available-for-sale securities, total, weighted-average yield	[2],[3]	1.80%
Held-to-maturity securities, maturing after five years through ten years, amortized cost	[3]	$ 30,703
Held-to-maturity securities, maturing after ten years, amortized cost	[3]	12,951
Held-to-maturity securities, Amortized Cost	[3]	43,654
Held-to-maturity securities, maturing after five years through ten years, fair value	[3]	28,569
Held-to-maturity securities, maturing after ten years, fair value	[3]	12,003
Held-to-maturity securities, total, fair value	[3]	$ 40,572
Held-to-maturity securities, maturing after five years through ten years, weighted-average maturity in years	[3]	9 years 6 months
Held-to-maturity securities, maturing after ten years, weighted-average maturity in years	[3]	10 days 7 hours
Held-to-maturity securities, total, weighted-average maturity in years	[3]	9 years 8 months 12 days
Held-to-maturity securities, maturing after five years through ten years, weighted-average yield	[2],[3]	1.58%
Held-to-maturity securities, maturing after ten years, weighted-average yield	[2],[3]	1.78%
Held-to-maturity securities, total, weighted-average yield	[2],[3]	1.64%
Asset-Backed Securities [Member]
Contractual Maturities of Investment Securities [Line Items]
Available-for-sale securities, maturing after one year through five years, amortized cost	[3]	$ 2
Available-for-sale securities, maturing after five years through ten years, amortized cost	[3]	2
Available-for-sale securities, Amortized Cost		4	[3]	62
Available-for-sale securities, maturing after one year through five years, fair value	[3]	3
Available-for-sale securities, maturing after five years through ten years, fair value	[3]	2
Available-for-sale securities, maturing after ten years, fair value	[3]	2
Available-for-sale securities, total, fair value		$ 7	[3]	66
Available-for-sale securities, maturing in one year or less, weighted-average maturity in years	[3]	6 months
Available-for-sale securities, maturing after one year through five years, weighted-average maturity in years	[3]	3 years
Available-for-sale securities, maturing after five years through ten years, weighted-average maturity in years	[3]	6 years
Available-for-sale securities, maturing after ten years, weighted- average maturity in years	[3]	13 years
Available-for-sale securities, total, weighted-average maturity in years	[3]	4 years 1 month 6 days
Available-for-sale securities, maturing in one year or less, weighted-average yield	[2],[3]	2.69%
Available-for-sale securities, maturing after one year through five years, weighted-average yield	[2],[3]	1.91%
Available-for-sale securities, maturing after five years through ten years, weighted-average yield	[2],[3]	2.13%
Available-for-sale securities, maturing after ten years, weighted-average yield	[2],[3]	2.41%
Available-for-sale securities, total, weighted-average yield	[2],[3]	2.00%
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	[4],[5]	$ 409
Available-for-sale securities, maturing after one year through five years, amortized cost	[4],[5]	3,046
Available-for-sale securities, maturing after five years through ten years, amortized cost	[4],[5]	3,326
Available-for-sale securities, maturing after ten years, amortized cost	[4],[5]	3,920
Available-for-sale securities, Amortized Cost		10,701	[4],[5]	10,130
Available-for-sale securities, maturing in one year or less, fair value	[4],[5]	412
Available-for-sale securities, maturing after one year through five years, fair value	[4],[5]	3,120
Available-for-sale securities, maturing after five years through ten years, fair value	[4],[5]	3,335
Available-for-sale securities, maturing after ten years, fair value	[4],[5]	3,407
Available-for-sale securities, total, fair value		$ 10,274	[4],[5]	10,717
Available-for-sale securities, maturing in one year or less, weighted-average maturity in years	[4],[5]	4 months 24 days
Available-for-sale securities, maturing after one year through five years, weighted-average maturity in years	[4],[5]	4 years
Available-for-sale securities, maturing after five years through ten years, weighted-average maturity in years	[4],[5]	6 years 6 months
Available-for-sale securities, maturing after ten years, weighted- average maturity in years	[4],[5]	17 years 1 month 6 days
Available-for-sale securities, total, weighted-average maturity in years	[4],[5]	9 years 6 months
Available-for-sale securities, maturing in one year or less, weighted-average yield	[2],[4],[5]	4.74%
Available-for-sale securities, maturing after one year through five years, weighted-average yield	[2],[4],[5]	4.34%
Available-for-sale securities, maturing after five years through ten years, weighted-average yield	[2],[4],[5]	3.83%
Available-for-sale securities, maturing after ten years, weighted-average yield	[2],[4],[5]	2.82%
Available-for-sale securities, total, weighted-average yield	[2],[4],[5]	3.64%
Other [Member]
Contractual Maturities of Investment Securities [Line Items]
Available-for-sale securities, maturing in one year or less, amortized cost		$ 7
Available-for-sale securities, Amortized Cost		7		7
Available-for-sale securities, maturing in one year or less, fair value		7
Available-for-sale securities, total, fair value		$ 7		$ 7
Available-for-sale securities, maturing in one year or less, weighted-average maturity in years		1 month 6 days
Available-for-sale securities, total, weighted-average maturity in years		1 month 6 days
Available-for-sale securities, maturing in one year or less, weighted-average yield	[2]	2.07%
Available-for-sale securities, total, weighted-average yield	[2]	2.07%

[1] The weighted-average maturity of total held-to-maturity investment securities was 7.4 years at December 31, 2021, with a corresponding weighted-average yield of 1.45 percent. The weighted-average maturity of total available-for-sale investment securities was 5.5 years at December 31, 2021, with a corresponding weighted-average yield of 1.73 percent.

[2] 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.

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

[4] 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.

[5] 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.