Earnings Per Share - Computation of Basic and Diluted Earnings per Share (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions		3 Months Ended		6 Months Ended
		Mar. 31, 2020	Mar. 31, 2019	Mar. 31, 2020	Mar. 31, 2019
Numerator
Numerator for basic and diluted EPS - Income (loss) from continuing operations		$ (575)	$ 45	$ (541)	$ (26)
Denominator
Denominator for basic EPS - Weighted-average common shares outstanding		61	63	61	63
Share based awards convertible to common shares	[1]	0	1	0	0
Denominator for diluted EPS - Adjusted weighted-average shares and assumed conversions		61	64	61	63
PER SHARE DATA
Basic		$ (9.48)	$ 0.72	$ (8.93)	$ (0.41)
Diluted		$ (9.48)	$ 0.71	$ (8.93)	$ (0.41)

[1] As a result of the loss from continuing operations attributable to Ashland during the three and six months ended March 31,2020, respectively and the six months ended March 31, 2019, the effect of the share-based awards convertible to common shares would be antidilutive and have been excluded from the diluted EPS calculation.