Post-retirement benefits - Summary of total amount recognised in other comprehensive income before tax (Detail) - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Disclosure of net defined benefit liability (asset) [Abstract]
Actuarial gains/(losses)	$ 3,410	$ 655	$ (1,242)
Loss on application of asset ceiling	(1)	0	0
Return on assets, net of interest on assets	(2,831)	371	768
Re-measurement gains/(losses) on pension and post-retirement healthcare plans	$ 578	$ 1,026	$ (474)

The amount of other comprehensive income, before tax, related to gains (losses) on remeasurements of defined benefit plans, which comprise actuarial gains and losses; the return on plan assets, excluding amounts included in net interest on the net defined benefit liability (asset); and any change in the effect of the asset ceiling, excluding amounts included in net interest on the net defined benefit liability (asset). [Refer: Other comprehensive income; Defined benefit plans [member]; Plan assets [member]; Net defined benefit liability (asset)] [Contrast: Decrease (increase) in net defined benefit liability (asset) resulting from gain (loss) on remeasurement in other comprehensive income]

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