Benefit Plans - Additional Information (Detail) - USD ($) $ in Millions	1 Months Ended	12 Months Ended
	Oct. 31, 2018	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2016
Defined Benefit Plan Disclosure [Line Items]
Percent of total assets domestic plans		69.00%
Cost of the savings incentive plan		$ 89	$ 67	$ 61
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		28.00%
Equity securities
Defined Benefit Plan Disclosure [Line Items]
Company's Target allocation percentage for asset mix		32.00%
Pension Plans
Defined Benefit Plan Disclosure [Line Items]
Pension plan assets at fair value		$ 2,642	1,932	1,855
Pension plan projected benefit obligations		3,246	2,647	$ 2,719
Estimated net actuarial loss that will be amortized from accumulated other comprehensive income		(79)
Estimated prior service credit costs that will be amortized from accumulated other comprehensive income		(14)
Employer contribution		400	54
Other Postretirement Benefits
Defined Benefit Plan Disclosure [Line Items]
Estimated prior service credit costs that will be amortized from accumulated other comprehensive income		(5)
United States | Pension Plans
Defined Benefit Plan Disclosure [Line Items]
Pension plan assets at fair value		1,821	1,254
Employer contribution		287
United States | Pension Plans | Equity securities
Defined Benefit Plan Disclosure [Line Items]
Pension plan assets at fair value		536	369
Foreign Plans | Pension Plans
Defined Benefit Plan Disclosure [Line Items]
Pension plan assets at fair value		821	678
Pension plan projected benefit obligations		$ 1,064	917
Percent of total plan assets foreign plans		31.00%
Foreign Plans | Pension Plans | Equity securities
Defined Benefit Plan Disclosure [Line Items]
Pension plan assets at fair value		$ 314	256
Domestic Plan [Member] | Other Postretirement Benefits
Defined Benefit Plan Disclosure [Line Items]
Pension plan projected benefit obligations		$ 148	$ 165
Subsequent Event [Member] | United States | Pension Plans
Defined Benefit Plan Disclosure [Line Items]
Employer contribution	$ 200