Pension and Other Postretirement Benefits - Weighted Average Actuarial Assumptions (Detail)	12 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2018
U.S. Plans
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Discount rate for benefit obligation	2.88%	3.26%	4.23%
Discount rate for net periodic benefit cost	3.27%	4.23%	3.84%
Expected long-term rate of return on plan assets	7.00%	7.00%	7.00%
Non-U.S. Plans
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Discount rate for benefit obligation	1.60%	1.80%	2.90%
Discount rate for net periodic benefit cost	1.80%	2.90%	2.70%
Expected long-term rate of return on plan assets	3.00%	3.00%	4.25%
Rate of increase in compensation levels for:
Benefit obligation	2.50%	2.50%	3.20%
Net periodic benefit cost	2.50%	2.50%	3.20%