Commitments and Contingencies - Additional Information (Detail) - USD ($) $ in Millions	3 Months Ended	6 Months Ended	12 Months Ended
Mar. 31, 2021	Jun. 30, 2019	Mar. 31, 2021	Sep. 30, 2020
Loss Contingencies [Line Items]
Reserves for environmental liabilities	$ 112.0		$ 112.0	$ 130.0
Accrued Environmental Loss Contingencies, Current	46.0		46.0	61.0
Accrued Environmental Loss Contingencies, Noncurrent	66.0		66.0	69.0
Conditional asset retirement obligations	29.0		29.0	29.0
Estimated asbestos related net liability on a discounted basis	93.0		93.0	115.0
Liability for Asbestos and Environmental Claims, Gross	470.0		470.0	483.0
Restricted Cash and Investments	377.0		377.0	368.0
Restricted Cash and Cash Equivalents	11.0		11.0	9.0
Insurance Recoveries			62.0	68.0
Insurable liabilities	366.0		366.0	363.0
Insurance Settlements Receivable	21.0		21.0	21.0
Insurance Settlements Receivable, Current	5.0		5.0	5.0
Insurance Settlements Receivable, Noncurrent	16.0		16.0	16.0
Litigation Settlement, Amount Awarded to Other Party	17.5
Asbestos Issue [Member]
Loss Contingencies [Line Items]
Restricted Cash and Cash Equivalents	11.0		11.0	9.0
Restricted Investments	304.0		304.0	291.0
Accrued Compensation and Benefits [Member]
Loss Contingencies [Line Items]
Insurable liabilities	23.0		23.0	22.0
Other Current Assets
Loss Contingencies [Line Items]
Restricted Cash and Investments	22.0		22.0	39.0
Other Noncurrent Assets
Loss Contingencies [Line Items]
Restricted Cash and Investments	355.0		355.0	329.0
Other Noncurrent Liabilities [Member]
Loss Contingencies [Line Items]
Liability for Asbestos and Environmental Claims, Gross	421.0		421.0	434.0
Insurable liabilities	253.0		253.0	258.0
Other Current Liabilities
Loss Contingencies [Line Items]
Liability for Asbestos and Environmental Claims, Gross	49.0		49.0	49.0
Insurable liabilities	$ 90.0		$ 90.0	$ 83.0
Stanton Street Facility, Marinette, WI [Member]
Loss Contingencies [Line Items]
Environmental Remediation Expense		$ 140.0

Estimated asbestos related net liability on a discounted basis

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