Commitments and Contingencies - Additional Information (Detail) - USD ($) $ in Millions	3 Months Ended	12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018
Loss Contingencies [Line Items]
Estimated asbestos related net liability on a discounted basis	$ 194	$ 173
Reserves for environmental liabilities	32	37
Conditional asset retirement obligations	29	29
Accrued Environmental Loss Contingencies, Current	13	10
Accrued Environmental Loss Contingencies, Noncurrent	19	27
Liability for Asbestos and Environmental Claims, Gross	546	550
Restricted Cash and Investments	352	377
Restricted Cash and Cash Equivalents	20	15
Insurance Recoveries	89	90
Insurable liabilities	415	417
Insurance Settlements Receivable, Current	6
Insurance Settlements Receivable	26
Insurance Settlements Receivable, Noncurrent	20
Asbestos Issue [Member]
Loss Contingencies [Line Items]
Restricted Cash and Cash Equivalents	20	6
Restricted Investments	243	281
Accrued Compensation and Benefits [Member]
Loss Contingencies [Line Items]
Insurable liabilities	22	22
Other Current Assets
Loss Contingencies [Line Items]
Restricted Cash and Investments	33	33
Other Noncurrent Assets
Loss Contingencies [Line Items]
Restricted Cash and Investments	319	344
Other Noncurrent Liabilities [Member]
Loss Contingencies [Line Items]
Liability for Asbestos and Environmental Claims, Gross	491	495
Insurable liabilities	299	300
Other Current Liabilities
Loss Contingencies [Line Items]
Liability for Asbestos and Environmental Claims, Gross	55	55
Insurable liabilities	$ 94	$ 95