v3.26.1
Fair Value Measurements - Summary of Fair Value Hierarchy Master Trust Investment Assets at Fair Value (Details) - EBP 020 - USD ($)
$ in Thousands
Dec. 31, 2025
Dec. 31, 2024
EBP, Investment, Fair Value and NAV [Line Items]    
Investments at fair value $ 1,369,226 $ 1,303,068
Money Market Fund    
EBP, Investment, Fair Value and NAV [Line Items]    
Investments at fair value 252 397
Ashland Inc. Common Stock    
EBP, Investment, Fair Value and NAV [Line Items]    
Investments at fair value 28,860 38,372
Shares of Registered Investment Companies    
EBP, Investment, Fair Value and NAV [Line Items]    
Investments at fair value 171,539 162,677
Stable Value Fund Money Market Fund    
EBP, Investment, Fair Value and NAV [Line Items]    
Investments at fair value 3,577 1,793
Investment Excluding Common Collective Trust    
EBP, Investment, Fair Value and NAV [Line Items]    
Investments at fair value 204,228 203,239
Common/Collective Trusts    
EBP, Investment, Fair Value and NAV [Line Items]    
Investments at fair value 1,164,998 1,099,829
Level 1    
EBP, Investment, Fair Value and NAV [Line Items]    
Investments at fair value 204,228 203,239
Level 1 | Money Market Fund    
EBP, Investment, Fair Value and NAV [Line Items]    
Investments at fair value 252 397
Level 1 | Ashland Inc. Common Stock    
EBP, Investment, Fair Value and NAV [Line Items]    
Investments at fair value 28,860 38,372
Level 1 | Shares of Registered Investment Companies    
EBP, Investment, Fair Value and NAV [Line Items]    
Investments at fair value 171,539 162,677
Level 1 | Stable Value Fund Money Market Fund    
EBP, Investment, Fair Value and NAV [Line Items]    
Investments at fair value 3,577 1,793
Level 1 | Investment Excluding Common Collective Trust    
EBP, Investment, Fair Value and NAV [Line Items]    
Investments at fair value 204,228 203,239
Level 1 | Common/Collective Trusts    
EBP, Investment, Fair Value and NAV [Line Items]    
Investments at fair value 0 0
Level 2    
EBP, Investment, Fair Value and NAV [Line Items]    
Investments at fair value 0 0
Level 2 | Money Market Fund    
EBP, Investment, Fair Value and NAV [Line Items]    
Investments at fair value 0 0
Level 2 | Ashland Inc. Common Stock    
EBP, Investment, Fair Value and NAV [Line Items]    
Investments at fair value 0 0
Level 2 | Shares of Registered Investment Companies    
EBP, Investment, Fair Value and NAV [Line Items]    
Investments at fair value 0 0
Level 2 | Stable Value Fund Money Market Fund    
EBP, Investment, Fair Value and NAV [Line Items]    
Investments at fair value 0 0
Level 2 | Investment Excluding Common Collective Trust    
EBP, Investment, Fair Value and NAV [Line Items]    
Investments at fair value 0 0
Level 2 | Common/Collective Trusts    
EBP, Investment, Fair Value and NAV [Line Items]    
Investments at fair value 0 0
Level 3    
EBP, Investment, Fair Value and NAV [Line Items]    
Investments at fair value 0 0
Level 3 | Money Market Fund    
EBP, Investment, Fair Value and NAV [Line Items]    
Investments at fair value 0 0
Level 3 | Ashland Inc. Common Stock    
EBP, Investment, Fair Value and NAV [Line Items]    
Investments at fair value 0 0
Level 3 | Shares of Registered Investment Companies    
EBP, Investment, Fair Value and NAV [Line Items]    
Investments at fair value 0 0
Level 3 | Stable Value Fund Money Market Fund    
EBP, Investment, Fair Value and NAV [Line Items]    
Investments at fair value 0 0
Level 3 | Investment Excluding Common Collective Trust    
EBP, Investment, Fair Value and NAV [Line Items]    
Investments at fair value 0 0
Level 3 | Common/Collective Trusts    
EBP, Investment, Fair Value and NAV [Line Items]    
Investments at fair value $ 0 $ 0