Commitments and Contingencies - Additional Information (Detail) - USD ($) $ in Millions	3 Months Ended	9 Months Ended	12 Months Ended
	Jun. 30, 2019	Jun. 30, 2020	Sep. 30, 2019
Loss Contingencies [Line Items]
Reserves for environmental liabilities		$ 136	$ 159
Accrued Environmental Loss Contingencies, Current		45	52
Accrued Environmental Loss Contingencies, Noncurrent		91	107
Conditional asset retirement obligations		29	30
Estimated asbestos related net liability on a discounted basis		134	141
Liability for Asbestos and Environmental Claims, Gross		497	507
Restricted Cash and Investments		363	366
Restricted Cash and Cash Equivalents		13	16
Insurance Recoveries		69	77
Insurable liabilities		365	379
Insurance Settlements Receivable		23	23
Insurance Settlements Receivable, Current		5	5
Insurance Settlements Receivable, Noncurrent		18	18
Asbestos Issue [Member]
Loss Contingencies [Line Items]
Restricted Cash and Cash Equivalents		13	16
Restricted Investments		281	273
Accrued Compensation and Benefits [Member]
Loss Contingencies [Line Items]
Insurable liabilities		22	22
Other Current Assets
Loss Contingencies [Line Items]
Restricted Cash and Investments		43	46
Other Noncurrent Assets
Loss Contingencies [Line Items]
Restricted Cash and Investments		320	320
Other Noncurrent Liabilities [Member]
Loss Contingencies [Line Items]
Liability for Asbestos and Environmental Claims, Gross		447	457
Insurable liabilities		260	258
Other Current Liabilities
Loss Contingencies [Line Items]
Liability for Asbestos and Environmental Claims, Gross		50	50
Insurable liabilities		$ 83	$ 99
Stanton Street Facility, Marinette, WI [Member]
Loss Contingencies [Line Items]
Environmental Remediation Expense	$ 140