Goodwill - Movements in goodwill (Details) - Goodwill $ in Thousands	12 Months Ended
Sep. 30, 2024 CAD ($)
Reconciliation of changes in goodwill [abstract]
Beginning balance	$ 8,724,450
Business acquisitions	439,461
Foreign currency translation adjustment	306,465
Ending balance	9,470,376
Western and Southern Europe
Reconciliation of changes in goodwill [abstract]
Beginning balance	1,555,730
Business acquisitions	0
Foreign currency translation adjustment	79,977
Ending balance	1,635,707
U.S. Commercial and State Government
Reconciliation of changes in goodwill [abstract]
Beginning balance	1,258,377
Business acquisitions	42,055
Foreign currency translation adjustment	(2,175)
Ending balance	1,298,257
Canada
Reconciliation of changes in goodwill [abstract]
Beginning balance	1,142,148
Business acquisitions	0
Foreign currency translation adjustment	0
Ending balance	1,142,148
U.S. Federal
Reconciliation of changes in goodwill [abstract]
Beginning balance	1,090,703
Business acquisitions	397,406
Foreign currency translation adjustment	(3,813)
Ending balance	1,484,296
Scandinavia and Central Europe
Reconciliation of changes in goodwill [abstract]
Beginning balance	1,383,316
Business acquisitions	0
Foreign currency translation adjustment	79,654
Ending balance	1,462,970
U.K. and Australia
Reconciliation of changes in goodwill [abstract]
Beginning balance	896,809
Business acquisitions	0
Foreign currency translation adjustment	84,131
Ending balance	980,940
Finland, Poland and Baltics
Reconciliation of changes in goodwill [abstract]
Beginning balance	604,885
Business acquisitions	0
Foreign currency translation adjustment	32,292
Ending balance	637,177
Northwest and Central-East Europe
Reconciliation of changes in goodwill [abstract]
Beginning balance	532,129
Business acquisitions	0
Foreign currency translation adjustment	25,915
Ending balance	558,044
Asia Pacific
Reconciliation of changes in goodwill [abstract]
Beginning balance	260,353
Business acquisitions	0
Foreign currency translation adjustment	10,484
Ending balance	$ 270,837

The increase in intangible assets and goodwill resulting from acquisitions through business combinations. [Refer: Total for all business combinations [member]; Intangible assets and goodwill]

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Name IAS
-Number 38
-IssueDate 2024-01-01
-Paragraph 118
-Subparagraph e
-Clause i
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- Definition

The increase (decrease) in intangible assets and goodwill resulting from the net exchange differences arising when the financial statements are translated from the functional currency into a different presentation currency, including the translation of a foreign operation into the presentation currency of the reporting entity. [Refer: Intangible assets and goodwill]

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Name IAS
-Number 38
-IssueDate 2024-01-01
-Paragraph 118
-Subparagraph e
-Clause vii
-URI https://taxonomy.ifrs.org/xifrs-link?type=IAS&num=38&code=ifrs-tx-2024-en-r&anchor=para_118_e_vii&doctype=Standard
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- Definition

The amount of intangible assets and goodwill held by the entity. [Refer: Goodwill; Intangible assets other than goodwill]

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
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-IssueDate 2024-01-01
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