Employee benefits - Post-employment benefits plan (Details) - CAD ($) $ in Thousands	Sep. 30, 2022	Sep. 30, 2021
Disclosure of defined benefit plans [line items]
Defined benefit obligations	$ (724,527)	$ (1,134,554)
Fair value of plan assets	616,553	1,036,294
Surplus (deficit) in plan	(107,974)	(98,260)
Fair value of reimbursement rights	18,877	21,250
Net asset (liability) recognized in the balance sheet	(89,097)	(77,010)
Retirement benefits assets	47,071	106,228
Retirement benefits obligations	(155,045)	(204,488)
U.K.
Disclosure of defined benefit plans [line items]
Defined benefit obligations	(525,262)	(881,008)
Fair value of plan assets	571,909	986,359
Surplus (deficit) in plan	46,647	105,351
Fair value of reimbursement rights	0	0
Net asset (liability) recognized in the balance sheet	46,647	105,351
Retirement benefits assets	46,647	105,351
Retirement benefits obligations	0	0
France
Disclosure of defined benefit plans [line items]
Defined benefit obligations	(77,477)	(77,006)
Fair value of plan assets	0	661
Surplus (deficit) in plan	(77,477)	(76,345)
Fair value of reimbursement rights	0	0
Net asset (liability) recognized in the balance sheet	(77,477)	(76,345)
Retirement benefits assets	0	0
Retirement benefits obligations	(77,477)	(76,345)
Germany
Disclosure of defined benefit plans [line items]
Defined benefit obligations	(61,420)	(94,381)
Fair value of plan assets	11,028	12,234
Surplus (deficit) in plan	(50,392)	(82,147)
Fair value of reimbursement rights	18,495	20,823
Net asset (liability) recognized in the balance sheet	(31,897)	(61,324)
Retirement benefits assets	0	0
Retirement benefits obligations	(50,392)	(82,147)
Other
Disclosure of defined benefit plans [line items]
Defined benefit obligations	(60,368)	(82,159)
Fair value of plan assets	33,616	37,040
Surplus (deficit) in plan	(26,752)	(45,119)
Fair value of reimbursement rights	382	427
Net asset (liability) recognized in the balance sheet	(26,370)	(44,692)
Retirement benefits assets	424	877
Retirement benefits obligations	$ (27,176)	$ (45,996)

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

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

+ 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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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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