Employee benefits - Post-employment benefits plan (Details) - CAD ($) $ in Thousands	Sep. 30, 2023	Sep. 30, 2022
Disclosure of defined benefit plans [line items]
Defined benefit obligations	$ (774,654)	$ (749,943)
Fair value of plan assets	612,111	641,969
Surplus (deficit) in plan	(162,543)	(107,974)
Fair value of reimbursement rights	19,458	18,877
Net asset (liability) recognized in the balance sheet	(143,085)	(89,097)
Retirement benefits assets	836	47,071
Retirement benefits obligations	(163,379)	(155,045)
U.K.
Disclosure of defined benefit plans [line items]
Defined benefit obligations	(535,633)	(525,262)
Fair value of plan assets	536,226	571,909
Surplus (deficit) in plan	593	46,647
Fair value of reimbursement rights	0	0
Net asset (liability) recognized in the balance sheet	593	46,647
Retirement benefits assets	593	46,647
Retirement benefits obligations	0	0
France
Disclosure of defined benefit plans [line items]
Defined benefit obligations	(78,612)	(77,477)
Fair value of plan assets	0	0
Surplus (deficit) in plan	(78,612)	(77,477)
Fair value of reimbursement rights	0	0
Net asset (liability) recognized in the balance sheet	(78,612)	(77,477)
Retirement benefits assets	0	0
Retirement benefits obligations	(78,612)	(77,477)
Germany
Disclosure of defined benefit plans [line items]
Defined benefit obligations	(67,706)	(61,420)
Fair value of plan assets	11,747	11,028
Surplus (deficit) in plan	(55,959)	(50,392)
Fair value of reimbursement rights	19,082	18,495
Net asset (liability) recognized in the balance sheet	(36,877)	(31,897)
Retirement benefits assets	0	0
Retirement benefits obligations	(55,959)	(50,392)
Other
Disclosure of defined benefit plans [line items]
Defined benefit obligations	(92,703)	(85,784)
Fair value of plan assets	64,138	59,032
Surplus (deficit) in plan	(28,565)	(26,752)
Fair value of reimbursement rights	376	382
Net asset (liability) recognized in the balance sheet	(28,189)	(26,370)
Retirement benefits assets	243	424
Retirement benefits obligations	$ (28,808)	$ (27,176)

The amount of assets held by retirement benefit plans. [Refer: Defined benefit plans [member]]

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Name IAS
-Number 26
-IssueDate 2023-01-01
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- Definition

The present value, without deducting any plan assets, of expected future payments required to settle the obligation resulting from employee service in the current and prior periods. [Refer: Plan assets, at fair value]

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
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-IssueDate 2023-01-01
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No definition available.

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The amount of deficit or surplus in a defined benefit plan, adjusted for any effect of limiting a net defined benefit asset to the asset ceiling. [Refer: Defined benefit plans [member]]

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Name IAS
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-IssueDate 2023-01-01
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The amount of non-current net defined benefit liability. [Refer: Net defined benefit liability]

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
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-IssueDate 2023-01-01
-Paragraph 55
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- Definition

The fair value of defined benefit plan assets. Plan assets comprise assets held by a long-term employee benefit fund and qualifying insurance policies. [Refer: At fair value [member]]

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The amount of the entity's rights to the reimbursement by another party of some or all of the expenditure required to settle a defined benefit obligation recognised as a separate asset and measured at fair value. [Refer: At fair value [member]]

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Name IAS
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The fair value of any plan assets, less the present value of the defined benefit obligation. [Refer: Plan assets [member]]

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