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, 2021	Sep. 30, 2020	Sep. 30, 2019
Pension Benefits [Member] | U.S. Defined Benefit Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Discount rate	2.20%	3.10%	2.60%
Cash balance interest credit rate	2.00%	0.90%	0.90%
Discount rate - benefit obligation	2.50%	2.60%	4.20%
Discount rate - interest cost	1.40%	2.60%	3.90%
Expected long-term rate of return on plan assets		2.50%	6.30%
Cash balance interest credit rate	2.10%	0.90%	3.30%
Pension Benefits [Member] | Foreign Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Discount rate	2.10%	1.70%	1.80%
Initial health care cost trend rate	2.90%	3.00%	3.00%
Cash balance interest credit rate	1.70%	1.70%	1.90%
Discount rate - benefit obligation	1.70%	1.80%	2.40%
Discount rate - service cost	1.70%	1.80%	2.50%
Discount rate - interest cost	1.40%	1.60%	2.10%
Expected long-term rate of return on plan assets	4.60%	5.20%	4.90%
Initial health care cost trend rate	3.00%	3.00%	2.70%
Cash balance interest credit rate	1.70%	1.90%	2.00%
Postretirement Benefits [Member] | U.S. Defined Benefit Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Discount rate	2.40%	2.10%	2.90%
Initial health care cost trend rate	5.50%	6.00%	6.50%
Discount rate - benefit obligation	2.10%	2.90%	4.10%
Discount rate - service cost	1.50%	2.60%	4.00%
Discount rate - interest cost	1.40%	2.50%	3.70%
Initial health care cost trend rate	6.00%	6.50%	7.00%
Postretirement Benefits [Member] | Foreign Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Discount rate	2.80%	2.40%	2.40%
Initial health care cost trend rate	6.90%	6.90%	6.90%
Discount rate - benefit obligation	2.40%	2.40%	3.20%
Discount rate - service cost	3.00%	2.90%	3.50%
Discount rate - interest cost	2.10%	2.30%	3.10%
Initial health care cost trend rate	6.90%	6.90%	7.00%