Commitments and Contingencies - Additional Information (Detail) - USD ($) $ in Millions	3 Months Ended	9 Months Ended	12 Months Ended
Jun. 30, 2021	Jun. 30, 2019	Jun. 30, 2021	Sep. 30, 2020
Loss Contingencies [Line Items]
Reserves for environmental liabilities	$ 100.0		$ 100.0	$ 130.0
Accrued Environmental Loss Contingencies, Current	50.0		50.0	61.0
Accrued Environmental Loss Contingencies, Noncurrent	50.0		50.0	69.0
Conditional asset retirement obligations	29.0		29.0	29.0
Estimated asbestos related net liability on a discounted basis	78.0		78.0	115.0
Liability for Asbestos and Environmental Claims, Gross	466.0		466.0	483.0
Restricted Cash and Investments	388.0		388.0	368.0
Restricted Cash and Cash Equivalents	7.0		7.0	9.0
Insurance Recoveries			61.0	68.0
Insurable liabilities	359.0		359.0	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	7.0		7.0	9.0
Restricted Investments	320.0		320.0	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	19.0		19.0	39.0
Other Noncurrent Assets
Loss Contingencies [Line Items]
Restricted Cash and Investments	369.0		369.0	329.0
Other Noncurrent Liabilities [Member]
Loss Contingencies [Line Items]
Liability for Asbestos and Environmental Claims, Gross	417.0		417.0	434.0
Insurable liabilities	247.0		247.0	258.0
Other Current Liabilities
Loss Contingencies [Line Items]
Liability for Asbestos and Environmental Claims, Gross	49.0		49.0	49.0
Insurable liabilities	$ 89.0		$ 89.0	$ 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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