Employee compensation and benefits - The effect of changes in key assumptions on the principal plan (Details) - Pension Plan - Principal plan - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2025	Dec. 31, 2024
Discount rate
Disclosure of sensitivity analysis for actuarial assumptions [line items]
Percentage of reasonably possible increase in actuarial assumption	0.25%	0.25%
Percentage of reasonably possible decrease in actuarial assumption	0.25%	0.25%
Financial impact of increase	$ (477)	$ (473)
Financial impact of decrease	$ 496	$ 496
Inflation rate
Disclosure of sensitivity analysis for actuarial assumptions [line items]
Percentage of reasonably possible increase in actuarial assumption	0.25%	0.25%
Percentage of reasonably possible decrease in actuarial assumption	0.25%	0.25%
Financial impact of increase	$ 408	$ 389
Financial impact of decrease	$ (391)	$ (391)
Pension payments and deferred pensions
Disclosure of sensitivity analysis for actuarial assumptions [line items]
Percentage of reasonably possible increase in actuarial assumption	0.25%	0.25%
Percentage of reasonably possible decrease in actuarial assumption	0.25%	0.25%
Financial impact of increase	$ 504	$ 487
Financial impact of decrease	$ (478)	$ (478)
Pay
Disclosure of sensitivity analysis for actuarial assumptions [line items]
Percentage of reasonably possible increase in actuarial assumption	0.25%	0.25%
Percentage of reasonably possible decrease in actuarial assumption	0.25%	0.25%
Financial impact of increase	$ 7	$ 6
Financial impact of decrease	$ (6)	$ (6)
Change in mortality
Disclosure of sensitivity analysis for actuarial assumptions [line items]
Duration of reasonably possible increase in actuarial assumption	1 year	1 year
Financial impact of increase	$ 486	$ 483
Financial impact of decrease	$ (464)	$ (464)

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- Definition

Line items represent concepts included in a table. These concepts are used to disclose reportable information associated with members defined in one or many axes of the table.

+ References

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- Definition

The increase (decrease) in a defined benefit obligation that would have been caused by a decrease in a significant actuarial assumption that was reasonably possible at the end of the reporting period. [Refer: Actuarial assumptions [domain]]

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
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- Definition

The increase (decrease) in a defined benefit obligation that would have been caused by an increase in a significant actuarial assumption that was reasonably possible at the end of the reporting period. [Refer: Actuarial assumptions [domain]]

+ References

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- Definition

The reasonably possible percentage of the decrease in the actuarial assumption used to determine the present value of defined benefit obligation. [Refer: Actuarial assumptions [domain]]

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- Definition

The reasonably possible percentage of the increase in the actuarial assumption used to determine the present value of defined benefit obligation. [Refer: Actuarial assumptions [domain]]

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