v3.26.1
Equity Items - Summary of Reconciliation of Changes in Equity (Details) - USD ($)
$ / shares in Units, $ in Millions
 3 Months Ended 9 Months Ended
Jun. 30, 2026
Jun. 30, 2025
Jun. 30, 2026
Jun. 30, 2025
Reconciliation Of Changes In Stockholders Equity [Line Items]        
Balance, beginning of period     $ 1,904  
Balance, end of period $ 1,870 $ 1,889 $ 1,870 $ 1,889
Cash dividends declared per common share $ 0.42 $ 0.415 $ 1.25 $ 1.225
Common Stock and Paid in Capital [Member]        
Reconciliation Of Changes In Stockholders Equity [Line Items]        
Balance, beginning of period $ 13 $ 1 $ 7 $ 1
Common shares issued under stock incentive and other plans [1] 5 2 11 8
Common shares purchased under repurchase program [2],[3] 0 0 0 (6)
Balance, end of period 18 3 18 3
Retained earnings [Member]        
Reconciliation Of Changes In Stockholders Equity [Line Items]        
Balance, beginning of period 2,264 3,048 2,298 3,315
Net income (loss) 16 (742) 20 (877)
Dividends (20) (20) (57) (57)
Common shares purchased under repurchase program [2],[3] 0 0 0 (95)
Other 1 0 0 0
Balance, end of period 2,261 2,286 2,261 2,286
Accumulated other comprehensive loss [Member]        
Reconciliation Of Changes In Stockholders Equity [Line Items]        
Balance, beginning of period (411) (490) (401) (448)
Unrealized translation gain (loss) 4 91 (6) 46
Unrealized (loss) gain on commodity hedges (2) (1) (2) 2
Balance, end of period $ (409) $ (400) $ (409) $ (400)
[1] Common stock issued were 5,593 and 11,423 for the three months ended June 30, 2026 and 2025, respectively, and 83,605 and 139,824 for the nine months ended June 30, 2026 and 2025, respectively. Includes zero for both the three months ended June 30, 2026 and 2025, and $1 million and $4 million for the nine months ended June 30, 2026 and 2025, respectively, associated with stock-based compensation employee withholding taxes.
[2] Common stock repurchased were zero for each of the three and nine months ended June 30, 2026, and zero and 1,541,320 for the three and nine months ended June 30, 2025.
[3] Includes zero in excise tax on common stock repurchases for both the three and nine months ended June 30, 2026, and zero and $1 million for the three and nine months ended June 30, 2025. Ashland paid a total of $100 million for the nine months ended June 30, 2025 for common stock repurchases.