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Principal accounting policies - Additional information (Detail) | 12 Months Ended
--- | ---
Dec. 31, 2017 USD ($) Segment | Dec. 31, 2016 USD ($) | Dec. 31, 2015 USD ($)
Disclosure of initial application of standards or interpretations [Line Items] |  |  |
Derecognise a receivable | $ 235,000,000 |  |
Derecognise a receivable after tax | 164,000,000 |  |
Consolidated sales revenue | 40,030,000,000 | $ 33,781,000,000 | $ 34,829,000,000
Investment on money market fund | $ 7,800,000,000 |  |
Voting rights of associate to have significant infuluence | 20.00% |  |
Cash-generating units assessed for impairment | 0 |  |
Onerous contracts provision | $ 407,000,000 |  |
Operations with remaining lives | 10 years |  |
Number of operations | Segment | 10 |  |
Decreasing provision | $ 700,000,000 |  |
Provision for carrying value close-down, restoration and environmental | $ 9,983,000,000 | $ 8,722,000,000 |
Assumption of discount rates | 0.50% |  |
Risk free interest rate on provisions | 2.00% |  |
Intragroup loans | $ 21,000,000,000 |  |
Bottom of range [Member] |  |  |
Disclosure of initial application of standards or interpretations [Line Items] |  |  |
Percent of certainty | 50.00% |  |
Assessment period of market prices | three years |  |
Term of impairment review is under taken in relevant functional currency | five years |  |
Risk free interest rate on provisions | 0.50% |  |
Top of range [Member] |  |  |
Disclosure of initial application of standards or interpretations [Line Items] |  |  |
Percent of certainty | 90.00% |  |
Assessment period of market prices | five years |  |
Increase (decrease) due to voluntary changes in accounting policy [member] |  |  |
Disclosure of initial application of standards or interpretations [Line Items] |  |  |
Consolidated sales revenue | $ (15,000,000) |  |

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- Definition The amount of provision for onerous contracts. An onerous contract is a contract in which the unavoidable costs of meeting the obligation under the contract exceed the economic benefits expected to be received under it. [Refer: Other provisions] + References Reference 1: http://www.xbrl.org/2003/role/exampleRef -Note Expiry date 2019-01-01 -Name IAS -Number 37 -IssueDate 2016-01-13 -Section Example 8 An onerous contract -URI http://eifrs.ifrs.org/eifrs/XBRL?type=IAS&num=37&date=2016-03-30&anchor=sect_Example8Anonerouscontract&doctype=Illustrative%20Examples -URIDate 2016-03-31 Reference 2: http://www.xbrl.org/2003/role/exampleRef -Name IAS -Number 37 -IssueDate 2016-01-13 -Paragraph 66 -URI http://eifrs.ifrs.org/eifrs/XBRL?type=IAS&num=37&date=2016-03-30&anchor=para_66&doctype=Standard -URIDate 2016-03-31 + Details
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