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Income tax - Schedule of Unrecognized Tax Benefits (Detail) - USD ($) $ in Millions | 12 Months Ended
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Dec. 31, 2020 | Dec. 31, 2019 | Dec. 31, 2018
Deferred tax assets and liabilities [abstract] |  |  |
Balance of tax positions at beginning of the period | $ 28 | $ 44 | $ 80
Adoption effects of IFRIC 23 credited to retained earnings (note 2.1) |  | (6) |
Additions for tax positions of prior periods |  |  | 1
Additions for tax positions of current period | 3 | 4 | 6
Reductions for tax positions related to prior periods and other items | (1) | (13) | (2)
Settlements and reclassifications | (3) |  | (7)
Expiration of the statute of limitations | (2) | (2) | (32)
Foreign currency translation effects | 2 | 1 | (2)
Balance of tax positions at end of the period | $ 27 | $ 28 | $ 44

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- Definition Adoption effects of Ifric twenty three credited to retained earnings. + References No definition available. + Details
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