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Post-retirement benefits - Summary of funding policy and contributions to plans (Detail) - USD ($) $ in Millions | 12 Months Ended
--- | ---
Dec. 31, 2019 | Dec. 31, 2018 | Dec. 31, 2017
Disclosure of net defined benefit liability (asset) [Line Items] |  |  |
Contributions to defined benefit plans | $ 257 | $ 248 | $ 404
Contributions to defined contribution plans | 235 | 244 | 243
Contributions to industry-wide plans |  | 0 | 12
Total | 492 | $ 492 | $ 659
Pension benefits [member] |  |  |
Disclosure of net defined benefit liability (asset) [Line Items] |  |  |
Contributions to defined benefit plans | 223 |  |
Contributions to defined contribution plans | 232 |  |
Total | 455 |  |
Other Benefits [member] |  |  |
Disclosure of net defined benefit liability (asset) [Line Items] |  |  |
Contributions to defined benefit plans | 34 |  |
Contributions to defined contribution plans | 3 |  |
Total | $ 37 |  |

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- Definition The decrease (increase) in net defined benefit liability (asset) resulting from contributions to a defined benefit plan by the employer. [Refer: Net defined benefit liability (asset); Defined benefit plans [member]] + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Name IAS -Number 19 -IssueDate 2019-01-01 -Paragraph 141 -Subparagraph f -URI http://eifrs.ifrs.org/eifrs/xifrs-link?type=IAS&num=19&code=ifrs-tx-2019-en-r&anchor=para_141_f&doctype=Standard -URIDate 2019-03-27 + Details
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- Definition The decrease (increase) in the net defined benefit liability (asset) resulting from contributions to a defined benefit plan. [Refer: Net defined benefit liability (asset); Defined benefit plans [member]] + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Name IAS -Number 19 -IssueDate 2019-01-01 -Paragraph 141 -Subparagraph f -URI http://eifrs.ifrs.org/eifrs/xifrs-link?type=IAS&num=19&code=ifrs-tx-2019-en-r&anchor=para_141_f&doctype=Standard -URIDate 2019-03-27 + Details
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- Definition Line items represent concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes of the table. + References No definition available. + Details
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- Definition Contributions to Defined Contribution Plans + References No definition available. + Details
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- Definition The decrease (increase) in the net defined benefit liability (asset) resulting from employer contributions to industry wide plans. + References No definition available. + Details
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- Details
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- Details
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