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Employee benefits - Defined benefit obligations (Details) - CAD ($) $ in Thousands | 12 Months Ended
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Sep. 30, 2025 | Sep. 30, 2024
Disclosure of net defined benefit liability (asset) [line items] |  |
Defined benefit liability (asset), beginning balance | $ 148,245 |
Current service cost | 16,290 | $ 14,165
Interest cost | 4,221 | 6,101
Past service cost | 2,521 | 0
Defined benefit liability (asset), ending balance | 123,420 | 148,245
U.K. |  |
Disclosure of net defined benefit liability (asset) [line items] |  |
Defined benefit liability (asset), beginning balance | (22,230) |
Defined benefit liability (asset), ending balance | (55,084) | (22,230)
France |  |
Disclosure of net defined benefit liability (asset) [line items] |  |
Defined benefit liability (asset), beginning balance | 95,366 |
Defined benefit liability (asset), ending balance | 99,215 | 95,366
GERMANY |  |
Disclosure of net defined benefit liability (asset) [line items] |  |
Defined benefit liability (asset), beginning balance | 42,816 |
Defined benefit liability (asset), ending balance | 44,080 | 42,816
Other |  |
Disclosure of net defined benefit liability (asset) [line items] |  |
Defined benefit liability (asset), beginning balance | 32,293 |
Defined benefit liability (asset), ending balance | 35,209 | 32,293
Present value of defined benefit obligation |  |
Disclosure of net defined benefit liability (asset) [line items] |  |
Defined benefit liability (asset), beginning balance | 897,948 | 774,654
Current service cost | 16,290 | 14,165
Interest cost | 41,181 | 41,686
Past service cost | 2,521 |
Business acquisitions | 7,860 |
Actuarial losses (gains) due to change in financial assumptions | (79,982) | 47,885
Actuarial losses (gains) due to change in demographic assumptions | (11,620) | 449
Actuarial (gains) losses due to experience | (17,225) | (6,315)
Plan participant contributions | 221 | 248
Benefits paid from the plan | (36,244) | (31,751)
Benefits paid directly by employer | (7,771) | (5,721)
Foreign currency translation adjustment | 38,092 | (62,648)
Defined benefit liability (asset), ending balance | 851,271 | 897,948
Present value of defined benefit obligation | Unfunded Plans |  |
Disclosure of net defined benefit liability (asset) [line items] |  |
Defined benefit liability (asset), beginning balance | 116,966 |
Defined benefit liability (asset), ending balance | 121,222 | 116,966
Present value of defined benefit obligation | Funded Plans |  |
Disclosure of net defined benefit liability (asset) [line items] |  |
Defined benefit liability (asset), beginning balance | 780,982 |
Defined benefit liability (asset), ending balance | 730,049 | 780,982
Present value of defined benefit obligation | U.K. |  |
Disclosure of net defined benefit liability (asset) [line items] |  |
Defined benefit liability (asset), beginning balance | 620,308 | 535,633
Current service cost | 336 | 946
Interest cost | 30,485 | 30,561
Past service cost | 0 |
Business acquisitions | 0 |
Actuarial losses (gains) due to change in financial assumptions | (61,738) | 29,444
Actuarial losses (gains) due to change in demographic assumptions | (10,673) | 0
Actuarial (gains) losses due to experience | (10,443) | (1,222)
Plan participant contributions | 57 | 86
Benefits paid from the plan | (32,269) | (27,712)
Benefits paid directly by employer | 0 | 0
Foreign currency translation adjustment | 19,893 | (52,572)
Defined benefit liability (asset), ending balance | 555,956 | 620,308
Present value of defined benefit obligation | U.K. | Unfunded Plans |  |
Disclosure of net defined benefit liability (asset) [line items] |  |
Defined benefit liability (asset), beginning balance | 0 |
Defined benefit liability (asset), ending balance | 0 | 0
Present value of defined benefit obligation | U.K. | Funded Plans |  |
Disclosure of net defined benefit liability (asset) [line items] |  |
Defined benefit liability (asset), beginning balance | 620,308 |
Defined benefit liability (asset), ending balance | 555,956 | 620,308
Present value of defined benefit obligation | France |  |
Disclosure of net defined benefit liability (asset) [line items] |  |
Defined benefit liability (asset), beginning balance | 95,366 | 78,612
Current service cost | 7,402 | 6,114
Interest cost | 3,234 | 3,378
Past service cost | 0 |
Business acquisitions | 7,860 |
Actuarial losses (gains) due to change in financial assumptions | (12,876) | 10,088
Actuarial losses (gains) due to change in demographic assumptions | (958) | 111
Actuarial (gains) losses due to experience | (6,719) | (5,100)
Plan participant contributions | 0 | 0
Benefits paid from the plan | 0 | 0
Benefits paid directly by employer | (2,793) | (2,033)
Foreign currency translation adjustment | 8,699 | (4,196)
Defined benefit liability (asset), ending balance | 99,215 | 95,366
Present value of defined benefit obligation | France | Unfunded Plans |  |
Disclosure of net defined benefit liability (asset) [line items] |  |
Defined benefit liability (asset), beginning balance | 95,366 |
Defined benefit liability (asset), ending balance | 99,215 | 95,366
Present value of defined benefit obligation | France | Funded Plans |  |
Disclosure of net defined benefit liability (asset) [line items] |  |
Defined benefit liability (asset), beginning balance | 0 |
Defined benefit liability (asset), ending balance | 0 | 0
Present value of defined benefit obligation | GERMANY |  |
Disclosure of net defined benefit liability (asset) [line items] |  |
Defined benefit liability (asset), beginning balance | 74,715 | 67,706
Current service cost | 376 | 373
Interest cost | 2,473 | 2,738
Past service cost | 0 |
Business acquisitions | 0 |
Actuarial losses (gains) due to change in financial assumptions | (2,563) | 4,948
Actuarial losses (gains) due to change in demographic assumptions | 0 | 0
Actuarial (gains) losses due to experience | (125) | (787)
Plan participant contributions | 0 | 0
Benefits paid from the plan | (156) | (503)
Benefits paid directly by employer | (4,069) | (3,192)
Foreign currency translation adjustment | 6,435 | (3,432)
Defined benefit liability (asset), ending balance | 77,086 | 74,715
Present value of defined benefit obligation | GERMANY | Unfunded Plans |  |
Disclosure of net defined benefit liability (asset) [line items] |  |
Defined benefit liability (asset), beginning balance | 0 |
Defined benefit liability (asset), ending balance | 0 | 0
Present value of defined benefit obligation | GERMANY | Funded Plans |  |
Disclosure of net defined benefit liability (asset) [line items] |  |
Defined benefit liability (asset), beginning balance | 74,715 |
Defined benefit liability (asset), ending balance | 77,086 | 74,715
Present value of defined benefit obligation | Other |  |
Disclosure of net defined benefit liability (asset) [line items] |  |
Defined benefit liability (asset), beginning balance | 107,559 | 92,703
Current service cost | 8,176 | 6,732
Interest cost | 4,989 | 5,009
Past service cost | 2,521 |
Business acquisitions | 0 |
Actuarial losses (gains) due to change in financial assumptions | (2,805) | 3,405
Actuarial losses (gains) due to change in demographic assumptions | 11 | 338
Actuarial (gains) losses due to experience | 62 | 794
Plan participant contributions | 164 | 162
Benefits paid from the plan | (3,819) | (3,536)
Benefits paid directly by employer | (909) | (496)
Foreign currency translation adjustment | 3,065 | (2,448)
Defined benefit liability (asset), ending balance | 119,014 | 107,559
Present value of defined benefit obligation | Other | Unfunded Plans |  |
Disclosure of net defined benefit liability (asset) [line items] |  |
Defined benefit liability (asset), beginning balance | 21,600 |
Defined benefit liability (asset), ending balance | 22,007 | 21,600
Present value of defined benefit obligation | Other | Funded Plans |  |
Disclosure of net defined benefit liability (asset) [line items] |  |
Defined benefit liability (asset), beginning balance | 85,959 |
Defined benefit liability (asset), ending balance | $ 97,007 | $ 85,959

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- Definition The decrease (increase) in a net defined benefit liability (asset) resulting from actuarial gains (losses) arising from changes in demographic assumptions that result in remeasurements of the net defined benefit liability (asset). Demographic assumptions deal with matters such as: (a) mortality; (b) rates of employee turnover, disability and early retirement; (c) the proportion of plan members with dependants who will be eligible for benefits; (d) the proportion of plan members who will select each form of payment option available under the plan terms; and (e) claim rates under medical plans. [Refer: Net defined benefit liability (asset)] + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Name IAS -Number 19 -IssueDate 2025-01-01 -Paragraph 141 -Subparagraph c -Clause ii -URI https://taxonomy.ifrs.org/xifrs-link?type=IAS&num=19&code=ifrs-tx-2025-en-r&anchor=para_141_c_ii&doctype=Standard -URIDate 2025-03-27 + Details
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- Definition The decrease (increase) in a net defined benefit liability (asset) resulting from actuarial gains (losses) arising from changes in financial assumptions that result in remeasurements of the net defined benefit liability (asset). Financial assumptions deal with items such as: (a) the discount rate; (b) benefit levels, excluding any cost of the benefits to be met by employees, and future salary; (c) in the case of medical benefits, future medical costs, including claim handling costs (ie the costs that will be incurred in processing and resolving claims, including legal and adjuster's fees); and (d) taxes payable by the plan on contributions relating to service before the reporting date or on benefits resulting from that service. [Refer: Net defined benefit liability (asset)] + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Name IAS -Number 19 -IssueDate 2025-01-01 -Paragraph 141 -Subparagraph c -Clause iii -URI https://taxonomy.ifrs.org/xifrs-link?type=IAS&num=19&code=ifrs-tx-2025-en-r&anchor=para_141_c_iii&doctype=Standard -URIDate 2025-03-27 + Details
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- Definition The decrease (increase) in a net defined benefit liability (asset) resulting from actuarial gains (losses) arising from experience adjustments that result in remeasurements of the net defined benefit liability (asset). Experience adjustments deal with the effects of differences between the previous actuarial assumptions and what has actually occurred. [Refer: Net defined benefit liability (asset)] + References Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef -Name IAS -Number 19 -IssueDate 2025-01-01 -Paragraph 141 -Subparagraph c -URI https://taxonomy.ifrs.org/xifrs-link?type=IAS&num=19&code=ifrs-tx-2025-en-r&anchor=para_141_c&doctype=Standard -URIDate 2025-03-27 + Details
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- Definition The decrease (increase) in the net defined benefit liability (asset) resulting from contributions to a defined benefit plan by plan participants. [Refer: Net defined benefit liability (asset); Defined benefit plans [domain]] + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Name IAS -Number 19 -IssueDate 2025-01-01 -Paragraph 141 -Subparagraph f -URI https://taxonomy.ifrs.org/xifrs-link?type=IAS&num=19&code=ifrs-tx-2025-en-r&anchor=para_141_f&doctype=Standard -URIDate 2025-03-27 + Details
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- Definition The increase (decrease) in the net defined benefit liability (asset) resulting from employee service in the current period. [Refer: Net defined benefit liability (asset)] + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Name IAS -Number 19 -IssueDate 2025-01-01 -Paragraph 141 -Subparagraph a -URI https://taxonomy.ifrs.org/xifrs-link?type=IAS&num=19&code=ifrs-tx-2025-en-r&anchor=para_141_a&doctype=Standard -URIDate 2025-03-27 Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Note Effective 2027-01-01 -Name IFRS -Number 19 -IssueDate 2025-01-01 -Paragraph 207 -Subparagraph a -URI https://taxonomy.ifrs.org/xifrs-link?type=IFRS&num=19&code=ifrs-tx-2025-en-r&anchor=para_207_a&doctype=Standard -URIDate 2025-03-27 Reference 3: http://www.xbrl.org/2003/role/disclosureRef -Note Effective 2027-01-01 -Name IFRS -Number 19 -IssueDate 2025-01-01 -Paragraph 207 -Subparagraph a -URI https://taxonomy.ifrs.org/xifrs-link?type=IFRS&num=19&code=ifrs-tx-2025-en-r&anchor=para_207_a&doctype=Standard -URIDate 2025-03-27 + Details
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- Definition The increase (decrease) in the net defined benefit liability (asset) resulting from business combinations and disposals. [Refer: Total for all business combinations [member]; Net defined benefit liability (asset)] + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Name IAS -Number 19 -IssueDate 2025-01-01 -Paragraph 141 -Subparagraph h -URI https://taxonomy.ifrs.org/xifrs-link?type=IAS&num=19&code=ifrs-tx-2025-en-r&anchor=para_141_h&doctype=Standard -URIDate 2025-03-27 + Details
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- Definition The increase (decrease) in the net defined benefit liability (asset) resulting from changes in foreign exchange rates. [Refer: Net defined benefit liability (asset)] + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Name IAS -Number 19 -IssueDate 2025-01-01 -Paragraph 141 -Subparagraph e -URI https://taxonomy.ifrs.org/xifrs-link?type=IAS&num=19&code=ifrs-tx-2025-en-r&anchor=para_141_e&doctype=Standard -URIDate 2025-03-27 + Details
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- Definition 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 -Name IAS -Number 19 -IssueDate 2025-01-01 -Paragraph 140 -Subparagraph a -URI https://taxonomy.ifrs.org/xifrs-link?type=IAS&num=19&code=ifrs-tx-2025-en-r&anchor=para_140_a&doctype=Standard -URIDate 2025-03-27 Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Note Effective 2027-01-01 -Name IFRS -Number 19 -IssueDate 2025-01-01 -Paragraph 206 -Subparagraph a -URI https://taxonomy.ifrs.org/xifrs-link?type=IFRS&num=19&code=ifrs-tx-2025-en-r&anchor=para_206_a&doctype=Standard -URIDate 2025-03-27 Reference 3: http://www.xbrl.org/2003/role/disclosureRef -Note Effective 2027-01-01 -Name IFRS -Number 19 -IssueDate 2025-01-01 -Paragraph 206 -Subparagraph a -URI https://taxonomy.ifrs.org/xifrs-link?type=IFRS&num=19&code=ifrs-tx-2025-en-r&anchor=para_206_a&doctype=Standard -URIDate 2025-03-27 + Details
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- Definition The increase (decrease) in the net defined benefit liability (asset) resulting from past service cost. Past service cost is the change in the present value of the defined benefit obligation for employee service in prior periods, resulting from a plan amendment (the introduction or withdrawal of, or changes to, a defined benefit plan) or a curtailment (a significant reduction by the entity in the number of employees covered by a plan). [Refer: Net defined benefit liability (asset); Defined benefit plans [domain]] + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Name IAS -Number 19 -IssueDate 2025-01-01 -Paragraph 141 -Subparagraph d -URI https://taxonomy.ifrs.org/xifrs-link?type=IAS&num=19&code=ifrs-tx-2025-en-r&anchor=para_141_d&doctype=Standard -URIDate 2025-03-27 Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Note Effective 2027-01-01 -Name IFRS -Number 19 -IssueDate 2025-01-01 -Paragraph 207 -Subparagraph d -URI https://taxonomy.ifrs.org/xifrs-link?type=IFRS&num=19&code=ifrs-tx-2025-en-r&anchor=para_207_d&doctype=Standard -URIDate 2025-03-27 Reference 3: http://www.xbrl.org/2003/role/disclosureRef -Note Effective 2027-01-01 -Name IFRS -Number 19 -IssueDate 2025-01-01 -Paragraph 207 -Subparagraph d -URI https://taxonomy.ifrs.org/xifrs-link?type=IFRS&num=19&code=ifrs-tx-2025-en-r&anchor=para_207_d&doctype=Standard -URIDate 2025-03-27 + Details
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- Definition The decrease (increase) in the net defined benefit liability (asset) resulting from payments from the plan. [Refer: Net defined benefit liability (asset)] + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Name IAS -Number 19 -IssueDate 2025-01-01 -Paragraph 141 -Subparagraph g -URI https://taxonomy.ifrs.org/xifrs-link?type=IAS&num=19&code=ifrs-tx-2025-en-r&anchor=para_141_g&doctype=Standard -URIDate 2025-03-27 Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Note Effective 2027-01-01 -Name IFRS -Number 19 -IssueDate 2025-01-01 -Paragraph 207 -Subparagraph f -URI https://taxonomy.ifrs.org/xifrs-link?type=IFRS&num=19&code=ifrs-tx-2025-en-r&anchor=para_207_f&doctype=Standard -URIDate 2025-03-27 Reference 3: http://www.xbrl.org/2003/role/disclosureRef -Note Effective 2027-01-01 -Name IFRS -Number 19 -IssueDate 2025-01-01 -Paragraph 207 -Subparagraph f -URI https://taxonomy.ifrs.org/xifrs-link?type=IFRS&num=19&code=ifrs-tx-2025-en-r&anchor=para_207_f&doctype=Standard -URIDate 2025-03-27 + Details
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