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Contingencies and commitments - Summary of capital commitments (Detail) - USD ($) $ in Millions | Dec. 31, 2018 | Dec. 31, 2017
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Capital Commitments |  |
Capital Commitments | $ 2,283 | $ 2,641
Due within 1 year [member] |  |
Capital Commitments |  |
Capital Commitments | 1,742 | 2,052
Between 1 and 3 years [member] |  |
Capital Commitments |  |
Capital Commitments | 439 | 531
Between 3 and 5 years [member] |  |
Capital Commitments |  |
Capital Commitments | 66 | 58
More than 5 years [member] |  |
Capital Commitments |  |
Capital Commitments | 36 |
Joint ventures [Member] |  |
Capital Commitments |  |
Capital Commitments | 116 | 29
Joint ventures [Member] | Due within 1 year [member] |  |
Capital Commitments |  |
Capital Commitments | 115 | $ 29
Joint ventures [Member] | Between 1 and 3 years [member] |  |
Capital Commitments |  |
Capital Commitments | $ 1 |

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- Definition The amount of future capital expenditures that the entity is committed to make. + References Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef -Name IAS -Number 1 -IssueDate 2017-01-01 -Paragraph 112 -Subparagraph c -URI http://eifrs.ifrs.org/eifrs/XBRL?type=IAS&num=1&date=2017-03-01&anchor=para_112_c&doctype=Standard -URIDate 2017-03-09 + Details
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