Fair Value Measurements - Carrying Value and Estimated Fair Value of Financial Instruments (Detail) - USD ($) $ in Millions		Mar. 31, 2024		Dec. 31, 2023		Mar. 31, 2023
Fair Value Disclosure, Asset and Liability, Not Measured at Fair Value [Line Items]
Federal funds sold and securities purchased under agreements to resell	[1]	$ 8,306		$ 13,878
Total loans, net		59,216	[1]	58,396	[1]	$ 58,874
Loans held for sale	[1]	453		339
Deposits		122,053	[1]	121,283	[1]	$ 122,168
Long-term debt	[1]	19,439		18,661
Level 1
Fair Value Disclosure, Asset and Liability, Not Measured at Fair Value [Line Items]
Short-term financial assets, net of allowance for credit losses		695		704
Federal funds sold and securities purchased under agreements to resell		0		0
Securities held-to-maturity, net of allowance for credit losses		1,878		0
Short-term financial liabilities		0		0
Deposits		0		0
Long-term debt		0		0
Level 1 | Commercial loans
Fair Value Disclosure, Asset and Liability, Not Measured at Fair Value [Line Items]
Total loans, net		0		0
Loans held for sale		0		0
Level 1 | Consumer loans
Fair Value Disclosure, Asset and Liability, Not Measured at Fair Value [Line Items]
Total loans, net		0		0
Level 2
Fair Value Disclosure, Asset and Liability, Not Measured at Fair Value [Line Items]
Short-term financial assets, net of allowance for credit losses		30,687		25,015
Federal funds sold and securities purchased under agreements to resell		8,306		13,878
Securities held-to-maturity, net of allowance for credit losses		12,839		14,689
Short-term financial liabilities		7,033		9,914
Deposits		119,959		119,465
Long-term debt		13,157		11,645
Level 2 | Commercial loans
Fair Value Disclosure, Asset and Liability, Not Measured at Fair Value [Line Items]
Total loans, net		0		0
Loans held for sale		189		89
Level 2 | Consumer loans
Fair Value Disclosure, Asset and Liability, Not Measured at Fair Value [Line Items]
Total loans, net		0		0
Level 3
Fair Value Disclosure, Asset and Liability, Not Measured at Fair Value [Line Items]
Short-term financial assets, net of allowance for credit losses		18		13
Federal funds sold and securities purchased under agreements to resell		0		0
Securities held-to-maturity, net of allowance for credit losses		0		0
Short-term financial liabilities		18		13
Deposits		0		0
Long-term debt		0		0
Level 3 | Commercial loans
Fair Value Disclosure, Asset and Liability, Not Measured at Fair Value [Line Items]
Total loans, net		40,744		40,557
Loans held for sale		0		0
Level 3 | Consumer loans
Fair Value Disclosure, Asset and Liability, Not Measured at Fair Value [Line Items]
Total loans, net		17,237		17,043
Carrying Value
Fair Value Disclosure, Asset and Liability, Not Measured at Fair Value [Line Items]
Short-term financial assets, net of allowance for credit losses		31,400		25,732
Federal funds sold and securities purchased under agreements to resell		8,306		13,878
Securities held-to-maturity, net of allowance for credit losses		15,294		15,076
Short-term financial liabilities		7,051		9,927
Deposits		119,969		119,462
Long-term debt		12,569		11,122
Carrying Value | Commercial loans
Fair Value Disclosure, Asset and Liability, Not Measured at Fair Value [Line Items]
Total loans, net		39,742		39,383
Loans held for sale		189		89
Carrying Value | Consumer loans
Fair Value Disclosure, Asset and Liability, Not Measured at Fair Value [Line Items]
Total loans, net		19,460		18,998
Fair Value
Fair Value Disclosure, Asset and Liability, Not Measured at Fair Value [Line Items]
Short-term financial assets, net of allowance for credit losses		31,400		25,732
Federal funds sold and securities purchased under agreements to resell		8,306		13,878
Securities held-to-maturity, net of allowance for credit losses		14,717		14,689
Short-term financial liabilities		7,051		9,927
Deposits		119,959		119,465
Long-term debt		13,157		11,645
Fair Value | Commercial loans
Fair Value Disclosure, Asset and Liability, Not Measured at Fair Value [Line Items]
Total loans, net		40,744		40,557
Loans held for sale		189		89
Fair Value | Consumer loans
Fair Value Disclosure, Asset and Liability, Not Measured at Fair Value [Line Items]
Total loans, net		$ 17,237		$ 17,043

[1] The following table summarizes assets and liabilities related to our consolidated variable interest entities ("VIEs") at March 31, 2024 and December 31, 2023. Assets and liabilities exclude intercompany balances that eliminate in consolidation. See Note 15, "Variable Interest Entities," for additional information. March 31, 2024December 31, 2023(in millions)AssetsOther assets$21 $23 Total assets$21 $23 LiabilitiesInterest, taxes and other liabilities$28 $17 Total liabilities$28 $17