Employee benefits - Post-employment benefits plan (Details) - CAD ($) $ in Thousands	Sep. 30, 2024	Sep. 30, 2023
Disclosure of defined benefit plans [line items]
Defined benefit obligations	$ (897,948)	$ (774,654)
Fair value of plan assets	730,028	612,111
Surplus (deficit) in plan	(167,920)	(162,543)
Fair value of reimbursement rights	19,675	19,458
Net asset (liability) recognized in the balance sheet	(148,245)	(143,085)
Retirement benefits assets	22,446	836
Retirement benefits obligations	(190,366)	(163,379)
U.K.
Disclosure of defined benefit plans [line items]
Defined benefit obligations	(620,308)	(535,633)
Fair value of plan assets	642,538	536,226
Surplus (deficit) in plan	22,230	593
Fair value of reimbursement rights	0	0
Net asset (liability) recognized in the balance sheet	22,230	593
Retirement benefits assets	22,230	593
Retirement benefits obligations	0	0
France
Disclosure of defined benefit plans [line items]
Defined benefit obligations	(95,366)	(78,612)
Fair value of plan assets	0	0
Surplus (deficit) in plan	(95,366)	(78,612)
Fair value of reimbursement rights	0	0
Net asset (liability) recognized in the balance sheet	(95,366)	(78,612)
Retirement benefits assets	0	0
Retirement benefits obligations	(95,366)	(78,612)
Germany
Disclosure of defined benefit plans [line items]
Defined benefit obligations	(74,715)	(67,706)
Fair value of plan assets	12,599	11,747
Surplus (deficit) in plan	(62,116)	(55,959)
Fair value of reimbursement rights	19,300	19,082
Net asset (liability) recognized in the balance sheet	(42,816)	(36,877)
Retirement benefits assets	0	0
Retirement benefits obligations	(62,116)	(55,959)
Other
Disclosure of defined benefit plans [line items]
Defined benefit obligations	(107,559)	(92,703)
Fair value of plan assets	74,891	64,138
Surplus (deficit) in plan	(32,668)	(28,565)
Fair value of reimbursement rights	375	376
Net asset (liability) recognized in the balance sheet	(32,293)	(28,189)
Retirement benefits assets	216	243
Retirement benefits obligations	$ (32,884)	$ (28,808)

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

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Name IAS
-Number 26
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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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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 [domain]]

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
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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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- 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
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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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