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Post-retirement benefits - Summary of total expense recognised in the income statement (Detail) - USD ($)
$ in Millions
 12 Months Ended
Dec. 31, 2023
Dec. 31, 2022
Dec. 31, 2021
Disclosure of net defined benefit liability (asset) [Line Items]      
Current employer service cost for defined benefit plans $ (79) $ (143) $ (167)
Past service credit/(cost) 87 0 (2)
Settlement losses 0 0 (3)
Net interest on net defined benefit liability (21) (36) (52)
Non-investment expenses paid from the plans (20) (13) (15)
Total defined benefit credit/(expense) (33) (192) (239)
Current employer service cost for defined contribution and industry-wide plans (416) (367) (315)
Total expense recognised in the income statement (449) $ (559) $ (554)
Pension benefits      
Disclosure of net defined benefit liability (asset) [Line Items]      
Current employer service cost for defined benefit plans (76)    
Past service credit/(cost) 88    
Settlement losses 0    
Net interest on net defined benefit liability 13    
Non-investment expenses paid from the plans (20)    
Total defined benefit credit/(expense) 5    
Current employer service cost for defined contribution and industry-wide plans (414)    
Total expense recognised in the income statement (409)    
Other benefits      
Disclosure of net defined benefit liability (asset) [Line Items]      
Current employer service cost for defined benefit plans (3)    
Past service credit/(cost) (1)    
Settlement losses 0    
Net interest on net defined benefit liability (34)    
Non-investment expenses paid from the plans 0    
Total defined benefit credit/(expense) (38)    
Current employer service cost for defined contribution and industry-wide plans (2)    
Total expense recognised in the income statement $ (40)