v3.26.1
Comprehensive income - Accumulated Other Comprehensive Income (Loss), Net (Detail) - USD ($)
$ in Millions
 3 Months Ended 6 Months Ended
Jun. 30, 2026
Jun. 30, 2025
Jun. 30, 2026
Jun. 30, 2025
AOCI Attributable to Parent, Net of Tax [Roll Forward]        
Beginning balance $ 27,972 $ 28,991 $ 29,177 $ 29,027
Total other comprehensive income (loss) (158) 125 (369) 379
Ending balance 27,946 28,525 27,946 28,525
Investment Securities        
AOCI Attributable to Parent, Net of Tax [Roll Forward]        
Beginning balance 6 (6) 155 (153)
Total other comprehensive income (loss) (99) 67 (248) 214
Ending balance (93) 61 (93) 61
Cash Flow Hedges        
AOCI Attributable to Parent, Net of Tax [Roll Forward]        
Beginning balance 7 7 67 (101)
Total other comprehensive income (loss) (58) 56 (118) 164
Ending balance (51) 63 (51) 63
Defined Benefit Plans        
AOCI Attributable to Parent, Net of Tax [Roll Forward]        
Beginning balance 60 96 61 98
Total other comprehensive income (loss) (1) (1) (2) (3)
Ending balance 59 95 59 95
Other        
AOCI Attributable to Parent, Net of Tax [Roll Forward]        
Beginning balance (7) (7) (6) (8)
Total other comprehensive income (loss) 0 3 (1) 4
Ending balance (7) (4) (7) (4)
Accumulated Other Comprehensive Income (Loss), Net        
AOCI Attributable to Parent, Net of Tax [Roll Forward]        
Beginning balance 66 90 277 (164)
Total other comprehensive income (loss) (158) 125 (369) 379
Ending balance $ (92) $ 215 $ (92) $ 215