Employee Benefit Plans - Assumptions Used to Determine Pension Benefit Obligations and Periodic Benefit Costs, Postretirement Benefit Obligations and Net Costs (Detail)	12 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2015
U.S. Pension Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Discount rate	3.60%	3.40%	4.20%
Discount rate - benefit obligation	3.40%	4.20%	4.00%
Discount rate - interest cost	2.70%	3.30%	4.00%
Expected long-term rate of return on plan assets	6.80%	7.50%	7.50%
Foreign Pension Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Discount rate	2.40%	1.80%	2.90%
Initial health care cost trend rate	2.70%	2.80%	2.80%
Discount rate - benefit obligation	1.80%	2.90%	3.00%
Discount rate - service cost	1.80%	2.80%	3.00%
Discount rate - interest cost	1.50%	2.40%	3.00%
Expected long-term rate of return on plan assets	4.70%	5.10%	5.40%
Initial health care cost trend rate	2.80%	2.80%	2.80%
U. S. Postretirement Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Discount rate	3.40%	3.00%	3.70%
Initial health care cost trend rate	7.00%	7.00%	6.50%
Discount rate - benefit obligation	3.00%	3.70%	3.80%
Discount rate - service cost	2.60%	3.40%	3.80%
Discount rate - interest cost	2.40%	2.80%	3.80%
Initial health care cost trend rate	7.00%	6.50%	7.00%
Foreign Postretirement Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Discount rate	3.10%	2.80%	3.90%
Initial health care cost trend rate	7.10%	6.10%	6.80%
Discount rate - benefit obligation	2.80%	3.90%	3.90%
Discount rate - service cost	3.20%	4.10%	3.90%
Discount rate - interest cost	2.60%	3.70%	3.90%
Initial health care cost trend rate	6.10%	6.80%	7.10%