Benefit Plans - Additional Information (Detail) - USD ($) $ in Millions	1 Months Ended	12 Months Ended
	Oct. 31, 2018	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2018
Defined Benefit Plan Disclosure [Line Items]
Percent of total assets domestic plans		69.00%
Cost of the savings incentive plan		$ 111	$ 126	$ 108
Fixed Income Funds
Defined Benefit Plan Disclosure [Line Items]
Company's Target allocation percentage for asset mix		40.00%
Diversified
Defined Benefit Plan Disclosure [Line Items]
Company's Target allocation percentage for asset mix		25.00%
Equity securities
Defined Benefit Plan Disclosure [Line Items]
Company's Target allocation percentage for asset mix		35.00%
Pension Plans
Defined Benefit Plan Disclosure [Line Items]
Pension plan assets at fair value		$ 3,045	2,926	2,642
Pension plan projected benefit obligations		3,953	3,731	$ 3,246
Employer contribution		42	258
Foreign Plans | Pension Plans
Defined Benefit Plan Disclosure [Line Items]
Pension plan assets at fair value		935	859
Pension plan projected benefit obligations		$ 1,321	1,244
Percent of total plan assets foreign plans		31.00%
United States | Pension Plans
Defined Benefit Plan Disclosure [Line Items]
Pension plan assets at fair value		$ 2,108	2,068
Employer contribution	$ 200
United States | Other Postretirement Benefits
Defined Benefit Plan Disclosure [Line Items]
Pension plan projected benefit obligations		$ 148	$ 153