Contingencies (Details) $ in Millions	1 Months Ended	3 Months Ended
	Nov. 30, 2012 item	Mar. 31, 2021 USD ($) a item	Sep. 30, 2020 USD ($)
Environmental remediation
Number of potentially responsible parties (PRPs) | item	50
Number of industrial companies and governmental entities under review | item	30
Number of PRP groups discussing allocation proposals | item	2
Total site remediation costs expected to cover river bottom area in excess of amount spent to date | $		$ 342
Area of river bottom to be remediated (in acres) | a		200
Project costs to date | $		$ 100
Number of subsidiaries assessed for disallowed deductions | item		1
Prior year collections of ICMS amounts realizable | $			$ 4
Other Current Liabilities And Other Noncurrent Liabilities
Environmental remediation
Estimated potential liability for all environmental matters | $		$ 28