EMPLOYEE BENEFITS - Net employee benefits expense (Details) - CAD ($) $ in Thousands	12 Months Ended
Mar. 31, 2025	Mar. 31, 2024
Employee benefits [Abstract]
Service cost	$ 921	$ 610
Interest cost	986	1,015
Total	1,907	1,625
Post-employment benefit expense, defined contribution plans	11,471	9,871
Net employee benefits expense	$ 13,378	$ 11,496

Employee benefits [Abstract]

No definition available.

Name:	ats_EmployeeBenefitsAbstract
Namespace Prefix:	ats_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

The expense of employee service in the current period arising from defined benefit plans. [Refer: Post-employment benefit expense in profit or loss, defined benefit plans] [Contrast: Increase in net defined benefit liability (asset) resulting from current service cost]

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Name IAS
-Number 19
-IssueDate 2024-01-01
-Paragraph 135
-Subparagraph b
-URI https://taxonomy.ifrs.org/xifrs-link?type=IAS&num=19&code=ifrs-tx-2024-en-r&anchor=para_135_b&doctype=Standard
-URIDate 2024-03-27

+ Details

Name:	ifrs-full_CurrentServiceCostDefinedBenefitPlans
Namespace Prefix:	ifrs-full_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

The amount of interest expense (income) arising from defined benefit plans. [Refer: Interest income (expense); Post-employment benefit expense in profit or loss, defined benefit plans] [Contrast: Increase (decrease) in net defined benefit liability (asset) resulting from interest expense (income)]

+ References

+ Details

Name:	ifrs-full_InterestExpenseIncomeDefinedBenefitPlans
Namespace Prefix:	ifrs-full_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

The amount of post-employment benefit expense included in profit or loss relating to defined benefit plans. [Refer: Profit (loss); Defined benefit plans [domain]] [Contrast: Increase (decrease) in net defined benefit liability (asset) resulting from expense (income) in profit or loss]

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Name IAS
-Number 19
-IssueDate 2024-01-01
-Paragraph 5
-URI https://taxonomy.ifrs.org/xifrs-link?type=IAS&num=19&code=ifrs-tx-2024-en-r&anchor=para_5&doctype=Standard
-URIDate 2024-03-27

Reference 2: http://www.xbrl.org/2009/role/commonPracticeRef
-Name IAS
-Number 19
-IssueDate 2024-01-01
-Paragraph 135
-Subparagraph b
-URI https://taxonomy.ifrs.org/xifrs-link?type=IAS&num=19&code=ifrs-tx-2024-en-r&anchor=para_135_b&doctype=Standard
-URIDate 2024-03-27

+ Details

Name:	ifrs-full_PostemploymentBenefitExpenseDefinedBenefitPlans
Namespace Prefix:	ifrs-full_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

The amount of post-employment benefit expense relating to defined contribution plans. Defined contribution plans are post-employment benefit plans under which an entity pays fixed contributions into a separate entity (a fund) and will have no legal or constructive obligation to pay further contributions if the fund does not hold sufficient assets to pay all employee benefits relating to employee service in the current and prior periods.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Name IAS
-Number 19
-IssueDate 2024-01-01
-Paragraph 53
-URI https://taxonomy.ifrs.org/xifrs-link?type=IAS&num=19&code=ifrs-tx-2024-en-r&anchor=para_53&doctype=Standard
-URIDate 2024-03-27

+ Details

Name:	ifrs-full_PostemploymentBenefitExpenseDefinedContributionPlans
Namespace Prefix:	ifrs-full_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

The amount of post-employment benefit expense included in profit or loss

+ References

+ Details

Name:	ifrs-full_PostemploymentBenefitExpenseInProfitOrLoss
Namespace Prefix:	ifrs-full_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration