Financial risk management activities - Reconciliation of deferred compensation asset (Details) - USD ($) $ in Millions |
6 Months Ended | 12 Months Ended |
|---|---|---|
Jun. 30, 2025 |
Dec. 31, 2024 |
|
| Deferred Compensation Asset [Roll Forward] | ||
| Opening balance | $ 48 | $ 48 |
| Unwinding of the asset | 2 | 4 |
| Changes in estimates - fair value adjustments | 13 | 3 |
| Part repayment - Mponeng | (18) | (6) |
| Consideration for Mansala and ABC | 34 | 0 |
| Translation | 0 | (1) |
| Closing balance | $ 79 | $ 48 |