Employee benefits - Post-employment benefits plan (Details) - CAD ($) $ in Thousands	Sep. 30, 2025	Sep. 30, 2024
Disclosure of defined benefit plans [line items]
Defined benefit obligations	$ (851,271)	$ (897,948)
Fair value of plan assets	707,712	730,028
Surplus (deficit) in plan	(143,559)	(167,920)
Fair value of reimbursement rights	20,139	19,675
Net asset (liability) recognized in the balance sheet	(123,420)	(148,245)
Retirement benefits assets	55,156	22,446
Retirement benefits obligations	(198,715)	(190,366)
U.K.
Disclosure of defined benefit plans [line items]
Defined benefit obligations	(555,956)	(620,308)
Fair value of plan assets	611,040	642,538
Surplus (deficit) in plan	55,084	22,230
Fair value of reimbursement rights	0	0
Net asset (liability) recognized in the balance sheet	55,084	22,230
Retirement benefits assets	55,084	22,230
Retirement benefits obligations	0	0
France
Disclosure of defined benefit plans [line items]
Defined benefit obligations	(99,215)	(95,366)
Fair value of plan assets	0	0
Surplus (deficit) in plan	(99,215)	(95,366)
Fair value of reimbursement rights	0	0
Net asset (liability) recognized in the balance sheet	(99,215)	(95,366)
Retirement benefits assets	0	0
Retirement benefits obligations	(99,215)	(95,366)
GERMANY
Disclosure of defined benefit plans [line items]
Defined benefit obligations	(77,086)	(74,715)
Fair value of plan assets	13,254	12,599
Surplus (deficit) in plan	(63,832)	(62,116)
Fair value of reimbursement rights	19,752	19,300
Net asset (liability) recognized in the balance sheet	(44,080)	(42,816)
Retirement benefits assets	0	0
Retirement benefits obligations	(63,832)	(62,116)
Other
Disclosure of defined benefit plans [line items]
Defined benefit obligations	(119,014)	(107,559)
Fair value of plan assets	83,418	74,891
Surplus (deficit) in plan	(35,596)	(32,668)
Fair value of reimbursement rights	387	375
Net asset (liability) recognized in the balance sheet	(35,209)	(32,293)
Retirement benefits assets	72	216
Retirement benefits obligations	$ (35,668)	$ (32,884)

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

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

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The amount of non-current net defined benefit liability. [Refer: Net defined benefit liability]

+ References

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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]]

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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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