Restructuring - Additional Information (Detail) - USD ($) $ in Millions	3 Months Ended		6 Months Ended		12 Months Ended
	Mar. 31, 2021	Dec. 31, 2020	Mar. 31, 2021	Mar. 31, 2020	Sep. 30, 2020
Restructuring Cost And Reserve [Line Items]
Restructuring charges	$ 1	$ 3
2020 Reorganization [Member]
Restructuring Cost And Reserve [Line Items]
Severance costs			$ 18	$ 12	$ 17
Accrued severance charges	2		2
Restructuring charges expected throughout rest of 2021 related to site demolition costs	1		1
Restructuring charges expected thereafter fiscal year related to site demolition costs	3		3
Restructuring cash payments of fiscal year	15			$ 7	13
Restructuring cash payments through the reminder of fiscal 2021	2
Restructuring future cash payments thereafter fiscal year	4		4
Purification Solutions Transformation Plan [Member]
Restructuring Cost And Reserve [Line Items]
Accrued severance charges	1		1
Restructuring cash payments of fiscal year			11		9
Restructuring cash payments through the reminder of fiscal 2021			2
Restructuring future cash payments thereafter fiscal year	2		2
Restructuring charges			14		$ 11
Purification Solutions Transformation Plan [Member] | Manufacturing Facility [Member]
Restructuring Cost And Reserve [Line Items]
Restructuring charges expected throughout rest of 2021 related to decommissioning costs	2		2
Restructuring charges expected thereafter fiscal year related to decommissioning costs	$ 1		$ 1