Post-retirement benefits - Summary of movement in present value of obligation (Details) - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2025	Dec. 31, 2024	Dec. 31, 2023
Changes in net defined benefit liability (asset) [abstract]
Beginning balance	$ (658)	$ (723)
Changes in financial assumptions gains/(losses)	(155)	(201)	$ 407
Currency exchange rate losses	(6)	29
Ending balance	(551)	(658)	(723)
Pension benefits
Changes in net defined benefit liability (asset) [abstract]
Beginning balance	(82)
Currency exchange rate losses	12
Ending balance	21	(82)
Other benefits
Changes in net defined benefit liability (asset) [abstract]
Beginning balance	(576)
Currency exchange rate losses	(18)
Ending balance	(572)	(576)
Present value of defined benefit obligation
Changes in net defined benefit liability (asset) [abstract]
Beginning balance	(10,763)	(11,795)
Current employer service costs	(80)	(83)
Past service (cost)/credit	(19)	(12)
Curtailments	4	0
Interest on obligation	(501)	(497)
Contributions by plan participants	(17)	(18)
Benefits paid	783	752
Experience (losses)/gains	(4)	2
Changes in financial assumptions gains/(losses)	148	256
Changes in demographic assumptions gains	11	(57)
Currency exchange rate losses	(619)	689
Ending balance	(11,057)	(10,763)	$ (11,795)
Present value of defined benefit obligation \| Pension benefits
Changes in net defined benefit liability (asset) [abstract]
Beginning balance	(10,187)
Current employer service costs	(77)
Past service (cost)/credit	(19)
Curtailments	3
Interest on obligation	(471)
Contributions by plan participants	(17)
Benefits paid	750
Experience (losses)/gains	(21)
Changes in financial assumptions gains/(losses)	149
Changes in demographic assumptions gains	6
Currency exchange rate losses	(601)
Ending balance	(10,485)	(10,187)
Present value of defined benefit obligation \| Other benefits
Changes in net defined benefit liability (asset) [abstract]
Beginning balance	(576)
Current employer service costs	(3)
Past service (cost)/credit	0
Curtailments	1
Interest on obligation	(30)
Contributions by plan participants	0
Benefits paid	33
Experience (losses)/gains	17
Changes in financial assumptions gains/(losses)	(1)
Changes in demographic assumptions gains	5
Currency exchange rate losses	(18)
Ending balance	$ (572)	$ (576)

The decrease (increase) in a net defined benefit liability (asset) resulting from actuarial gains (losses) arising from changes in demographic assumptions that result in remeasurements of the net defined benefit liability (asset). Demographic assumptions deal with matters such as: (a) mortality; (b) rates of employee turnover, disability and early retirement; (c) the proportion of plan members with dependants who will be eligible for benefits; (d) the proportion of plan members who will select each form of payment option available under the plan terms; and (e) claim rates under medical plans. [Refer: Net defined benefit liability (asset)]

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The decrease (increase) in a net defined benefit liability (asset) resulting from actuarial gains (losses) arising from changes in financial assumptions that result in remeasurements of the net defined benefit liability (asset). Financial assumptions deal with items such as: (a) the discount rate; (b) benefit levels, excluding any cost of the benefits to be met by employees, and future salary; (c) in the case of medical benefits, future medical costs, including claim handling costs (ie the costs that will be incurred in processing and resolving claims, including legal and adjuster's fees); and (d) taxes payable by the plan on contributions relating to service before the reporting date or on benefits resulting from that service. [Refer: Net defined benefit liability (asset)]

+ References

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The decrease (increase) in a net defined benefit liability (asset) resulting from actuarial gains (losses) arising from experience adjustments that result in remeasurements of the net defined benefit liability (asset). Experience adjustments deal with the effects of differences between the previous actuarial assumptions and what has actually occurred. [Refer: Net defined benefit liability (asset)]

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The decrease (increase) in the net defined benefit liability (asset) resulting from contributions to a defined benefit plan by plan participants. [Refer: Net defined benefit liability (asset); Defined benefit plans [domain]]

+ References

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The increase (decrease) in the net defined benefit liability (asset) resulting from employee service in the current period. [Refer: Net defined benefit liability (asset)]

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- Definition

The increase (decrease) in the net defined benefit liability (asset) resulting from changes in foreign exchange rates. [Refer: Net defined benefit liability (asset)]

+ References

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The amount of deficit or surplus in a defined benefit plan, adjusted for any effect of limiting a net defined benefit asset to the asset ceiling. [Refer: Defined benefit plans [domain]]

+ References

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The increase (decrease) in the net defined benefit liability (asset) resulting from past service cost. Past service cost is the change in the present value of the defined benefit obligation for employee service in prior periods, resulting from a plan amendment (the introduction or withdrawal of, or changes to, a defined benefit plan) or a curtailment (a significant reduction by the entity in the number of employees covered by a plan). [Refer: Net defined benefit liability (asset); Defined benefit plans [domain]]

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The decrease (increase) in the net defined benefit liability (asset) resulting from payments from the plan. [Refer: Net defined benefit liability (asset)]

+ References

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- Definition

Increase (Decrease) In Net Defined Benefit Liability (Asset) Resulting From Curtailments

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No definition available.

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