STOCK-BASED COMPENSATION - Schedule of Share-Based Payment Arrangement, Cost by Plan (Details) - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2025	Sep. 30, 2024	Sep. 30, 2023
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total stock compensation expense	$ 265	$ 260	$ 271
Income tax benefits recognized	35	32	28
Discontinued Operations
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total stock compensation expense	2	0	21
Continuing Operations
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total stock compensation expense	263	260	250
Performance shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total stock compensation expense	94	90	165
Restricted stock and restricted stock units
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total stock compensation expense	147	115	24
AspenTech stock-based compensation plans
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total stock compensation expense	$ 24	$ 55	$ 82