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Post-retirement benefits - Results summary of sensitivity analysis (Detail) - USD ($)
$ in Millions
12 Months Ended
Dec. 31, 2024
Dec. 31, 2023
Discount rate | Pension benefits    
Disclosure of sensitivity analysis for actuarial assumptions [line items]    
Increase of percentage points 50.00% 50.00%
Decrease of percentage points 50.00% 50.00%
Increase of actuarial assumption $ 419 $ 460
Decrease of actuarial assumption $ (487) $ (514)
Discount rate | Other benefits    
Disclosure of sensitivity analysis for actuarial assumptions [line items]    
Increase of percentage points 50.00% 50.00%
Decrease of percentage points 50.00% 50.00%
Increase of actuarial assumption $ 31 $ 31
Decrease of actuarial assumption $ (33) $ (33)
Long-term inflation | Pension benefits    
Disclosure of sensitivity analysis for actuarial assumptions [line items]    
Increase of percentage points 50.00% 50.00%
Decrease of percentage points 50.00% 50.00%
Increase of actuarial assumption $ (167) $ (183)
Decrease of actuarial assumption $ 160 $ 176
Long-term inflation | Other benefits    
Disclosure of sensitivity analysis for actuarial assumptions [line items]    
Increase of percentage points 50.00% 50.00%
Decrease of percentage points 50.00% 50.00%
Increase of actuarial assumption $ (9) $ (9)
Decrease of actuarial assumption $ 8 $ 8
Demographic – allowance for future improvements in longevity | Pension benefits    
Disclosure of sensitivity analysis for actuarial assumptions [line items]    
Increase in actuarial assumption of longevity trend 1 year 1 year
Decrease in actuarial assumption of longevity trend 1 year 1 year
Increase of actuarial assumption $ 221 $ 244
Decrease of actuarial assumption $ (232) $ (244)
Demographic – allowance for future improvements in longevity | Other benefits    
Disclosure of sensitivity analysis for actuarial assumptions [line items]    
Increase in actuarial assumption of longevity trend 1 year 1 year
Decrease in actuarial assumption of longevity trend 1 year 1 year
Increase of actuarial assumption $ 8 $ 7
Decrease of actuarial assumption $ (8) $ (7)