Benefit Plans - Additional Information (Detail) - USD ($) $ in Millions	1 Months Ended	12 Months Ended
	Oct. 31, 2018	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2017
Defined Benefit Plan Disclosure [Line Items]
Percent of total assets domestic plans		71.00%
Cost of the savings incentive plan		$ 126	$ 108	$ 83
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		$ 2,926	2,642	1,932
Pension plan projected benefit obligations		3,731	3,246	$ 2,647
Employer contribution		258	400
Foreign Plans | Pension Plans
Defined Benefit Plan Disclosure [Line Items]
Pension plan assets at fair value		859	821
Pension plan projected benefit obligations		$ 1,244	1,064
Percent of total plan assets foreign plans		29.00%
Foreign Plans | Pension Plans | Equity securities
Defined Benefit Plan Disclosure [Line Items]
Pension plan assets at fair value		$ 319	314
United States | Pension Plans
Defined Benefit Plan Disclosure [Line Items]
Pension plan assets at fair value		2,068	1,821
Employer contribution	$ 200
United States | Pension Plans | Equity securities
Defined Benefit Plan Disclosure [Line Items]
Pension plan assets at fair value		922	536
United States | Other Postretirement Benefits
Defined Benefit Plan Disclosure [Line Items]
Pension plan projected benefit obligations		$ 153	$ 148