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Retirement benefits - Defined Benefit Plans - Sensitivity Analysis of Actuarial Assumptions (Detail) - USD ($)
$ in Millions
Dec. 31, 2025
Dec. 31, 2024
Discount rate    
Disclosure of sensitivity analysis for actuarial assumptions [line items]    
Decrease in liabilities $ 5 $ 5
Increase in liabilities (5) (5)
Inflation rate    
Disclosure of sensitivity analysis for actuarial assumptions [line items]    
Decrease in liabilities 0 (1)
Increase in liabilities 0 0
Mortality rate    
Disclosure of sensitivity analysis for actuarial assumptions [line items]    
Increase in liabilities 3 2
Healthcare costs trend rate    
Disclosure of sensitivity analysis for actuarial assumptions [line items]    
Decrease in liabilities (1) (1)
Increase in liabilities $ 1 $ 1