Commitments and Contingencies - Additional Information (Detail) - USD ($) $ in Millions	3 Months Ended	12 Months Ended
	Mar. 31, 2017	Sep. 30, 2016
Loss Contingencies [Line Items]
Estimated asbestos related net liability on a discounted basis	$ 152	$ 148
Reserves for environmental liabilities	46	51
Conditional asset retirement obligations	72	74
Accrued Environmental Loss Contingencies, Current	9
Accrued Environmental Loss Contingencies, Noncurrent	37
Liability for Asbestos and Environmental Claims, Gross	540	548
Restricted Cash and Investments	388	400
Restricted Cash and Cash Equivalents	42	88
Insurance Recoveries	97	120
Insurable liabilities	468	422
Insurance Settlements Receivable, Current	30
Insurance Settlements Receivable	48
Insurance Settlements Receivable, Noncurrent	18	21
Asbestos Issue [Member]
Loss Contingencies [Line Items]
Restricted Cash and Cash Equivalents	33	16
Restricted Investments	258	264
Accrued Compensation and Benefits [Member]
Loss Contingencies [Line Items]
Insurable liabilities	32	28
Other Current Assets
Loss Contingencies [Line Items]
Restricted Cash and Investments	57	41
Other Noncurrent Assets
Loss Contingencies [Line Items]
Restricted Cash and Investments	331	359
Other Noncurrent Liabilities [Member]
Loss Contingencies [Line Items]
Liability for Asbestos and Environmental Claims, Gross	505	513
Insurable liabilities	350	334
Other Current Liabilities
Loss Contingencies [Line Items]
Liability for Asbestos and Environmental Claims, Gross	35	35
Insurable liabilities	$ 86	$ 60