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Significant accounting policies - Share-based compensation (Details) | 12 Months Ended
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Dec. 31, 2019
Performance shares | Tranche 2 | Bottom of range |
Disclosure of terms and conditions of share-based payment arrangement [line items] |
Share-based compensation arrangement vesting rights, percentage | 25.00%
Performance shares | Tranche 2 | Top of range |
Disclosure of terms and conditions of share-based payment arrangement [line items] |
Share-based compensation arrangement vesting rights, percentage | 150.00%
Performance Share Units (PSU) New Plan |
Disclosure of terms and conditions of share-based payment arrangement [line items] |
Vesting period | 3 years
Performance Share Units (PSU) New Plan | Tranche 2 | Bottom of range |
Disclosure of terms and conditions of share-based payment arrangement [line items] |
Share-based compensation arrangement vesting rights, percentage | 0.00%
Performance Share Units (PSU) New Plan | Tranche 2 | Top of range |
Disclosure of terms and conditions of share-based payment arrangement [line items] |
Share-based compensation arrangement vesting rights, percentage | 200.00%

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