Income tax - Unrecognised deferred tax balances (Details) - AUD ($) $ in Millions	12 Months Ended
Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2018
Income tax
Australian company tax rate (as a percent)	30.00%	30.00%	30.00%
Unrecognised deferred tax balances
Unrecognised deferred tax asset: Tax losses on revenue account	$ 335	$ 291
Unrecognised deferred tax liability: Gross retained earnings of subsidiaries which the Parent Entity does not intend to distribute in the foreseeable future	55	51
Parent Entity
Unrecognised deferred tax balances
Unrecognised deferred tax asset: Tax losses on revenue account	$ 264	$ 237

The applicable income tax rate.

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Name IAS
-Number 12
-IssueDate 2019-01-01
-Paragraph 81
-Subparagraph c
-Clause ii
-URI http://eifrs.ifrs.org/eifrs/xifrs-link?type=IAS&num=12&code=ifrs-tx-2019-en-r&anchor=para_81_c_ii&doctype=Standard
-URIDate 2019-03-27

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- Definition

The aggregate amount of temporary differences associated with investments in subsidiaries, branches and associates and interests in joint arrangements, for which deferred tax liabilities have not been recognised as a result of satisfying both of the following conditions: (a) the parent, investor, joint venturer or joint operator is able to control the timing of the reversal of the temporary difference; and (b) it is probable that the temporary difference will not reverse in the foreseeable future. [Refer: Associates [member]; Subsidiaries [member]; Temporary differences [member]; Investments in subsidiaries]

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Name IAS
-Number 12
-IssueDate 2019-01-01
-Paragraph 81
-Subparagraph f
-URI http://eifrs.ifrs.org/eifrs/xifrs-link?type=IAS&num=12&code=ifrs-tx-2019-en-r&anchor=para_81_f&doctype=Standard
-URIDate 2019-03-27

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- Definition

The amount of unused tax losses for which no deferred tax asset is recognised in the statement of financial position. [Refer: Unused tax losses [member]]

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Name IAS
-Number 12
-IssueDate 2019-01-01
-Paragraph 81
-Subparagraph e
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-URIDate 2019-03-27

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Line items represents concepts include in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes of the table.

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