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Post-retirement benefits - Summary of total amount recognised in other comprehensive income before tax (Detail) - USD ($)
$ in Millions
12 Months Ended
Dec. 31, 2023
Dec. 31, 2022
Dec. 31, 2021
Disclosure of net defined benefit liability (asset) [Abstract]      
Actuarial (losses)/gains $ (407) $ 3,410 $ 655
Impact of buy-in (216) 0 0
Return on assets, net of interest on assets 222 (2,831) 371
Losses on application of asset ceiling (60) (1) 0
Re-measurement (losses)/gains on pension and post-retirement healthcare plans $ (461) $ 578 [1] $ 1,026 [1]
[1] Comparative information has been restated to reflect the adoption of narrow-scope amendments to IAS 12. Refer to page 166 for details.