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 6 Months Ended
Jun. 30, 2026
Jun. 30, 2025
Jun. 30, 2026
Jun. 30, 2025
Derivative Instruments, Gain (Loss) [Line Items]        
Derivatives not designated as hedging instruments, derivatives $ 22 $ 9 $ 38 $ 18
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 Other costs of operations Other costs of operations
Derivatives in fair value hedging relationships, derivative $ (54) $ 54 $ (87) $ 147
Derivatives in fair value hedging relationships, hedged item 54 (55) 87 (147)
Interest Rate Contracts        
Derivative Instruments, Gain (Loss) [Line Items]        
Derivatives not designated as hedging instruments, derivatives 17 7 27 12
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 18 7 26  
Mortgage Banking Revenues | Not Designated as Hedging Instrument        
Derivative Instruments, Gain (Loss) [Line Items]        
Derivatives not designated as hedging instruments, derivatives 1   1  
Foreign exchange and other option and futures contracts        
Derivative Instruments, Gain (Loss) [Line Items]        
Derivatives not designated as hedging instruments, derivatives $ 5 $ 2 $ 11 $ 6