v3.26.1
Derivative financial instruments - Information about Fair Values of Derivative Instruments in Consolidated Statement of Income (Detail) - USD ($)
$ in Millions
 3 Months Ended
Mar. 31, 2026
Mar. 31, 2025
Derivative Instruments, Gain (Loss) [Line Items]    
Derivatives not designated as hedging instruments, derivatives $ 16 $ 9
Interest rate swap agreements | Designated as Hedging Instrument | Fair value hedges:    
Derivative Instruments, Gain (Loss) [Line Items]    
Derivatives in fair value hedging relationships, derivative (33) 93
Derivatives in fair value hedging relationships, hedged item $ 33 $ (92)
Interest rate swap agreements | Fixed Rate Long-Term Borrowings | Designated as Hedging Instrument | Fair value hedges:    
Derivative Instruments, Gain (Loss) [Line Items]    
Derivative, gain (loss), statement of income or comprehensive income [extensible enumeration] Other costs of operations Other costs of operations
Derivatives in fair value hedging relationships, derivative $ (33) $ 93
Derivatives in fair value hedging relationships, hedged item 33 (92)
Interest Rate Contracts    
Derivative Instruments, Gain (Loss) [Line Items]    
Derivatives not designated as hedging instruments, derivatives 10 5
Trading Account And Other Non Hedging Derivatives | Not Designated as Hedging Instrument    
Derivative Instruments, Gain (Loss) [Line Items]    
Derivatives not designated as hedging instruments, derivatives 8 5
Mortgage Banking Revenues | Not Designated as Hedging Instrument    
Derivative Instruments, Gain (Loss) [Line Items]    
Derivatives not designated as hedging instruments, derivatives   2
Foreign exchange and other option and futures contracts    
Derivative Instruments, Gain (Loss) [Line Items]    
Derivatives not designated as hedging instruments, derivatives $ 6 $ 4