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Post-retirement benefits - Summary of funding policy and contributions to plans (Detail) - USD ($)
$ in Millions
12 Months Ended
Dec. 31, 2021
Dec. 31, 2020
Dec. 31, 2019
Disclosure of net defined benefit liability (asset) [Line Items]      
Contributions to defined benefit plans $ 464 $ 201 $ 257
Contributions to defined contribution plans 311 261 235
Total 775 $ 462 $ 492
Pension benefits      
Disclosure of net defined benefit liability (asset) [Line Items]      
Contributions to defined benefit plans 425    
Contributions to defined contribution plans 309    
Total 734    
Other benefits      
Disclosure of net defined benefit liability (asset) [Line Items]      
Contributions to defined benefit plans 39    
Contributions to defined contribution plans 2    
Total $ 41