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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

X

- 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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X

- 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

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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

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- Definition

Contributions to Defined Contribution Plans

+ References

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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.

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