v3.26.1
Revenue - Summary of Percentage of Ashland's Total Consolidated Sales for Product (Details) - Sales Revenue [Member] - Product Concentration Risk [Member]
3 Months Ended 9 Months Ended
Jun. 30, 2026
Jun. 30, 2025
Jun. 30, 2026
Jun. 30, 2025
Cellulosics and PVP [Member]        
Revenue From Contracts With Customers [Line Items]        
Concentration risk percentage 64.00% 65.00% 64.00% 64.00%
Cellulosics [Member]        
Revenue From Contracts With Customers [Line Items]        
Concentration risk percentage 40.00% 40.00% 40.00% 39.00%
PVP [Member]        
Revenue From Contracts With Customers [Line Items]        
Concentration risk percentage 24.00% 25.00% 24.00% 25.00%