Benefit Plans - Change in Benefit Obligation, Change in Fair Value of Plan Assets (Detail) - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2018
Amounts recognized in the Consolidated Balance Sheets at September 30:
Long-term Employee Benefit Obligations	$ (1,435)	$ (1,272)
Pension Plans
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]
Beginning obligation	3,731	3,246
Service cost	153	134	$ 136
Interest cost	84	107	90
Plan amendments	0	(3)
Benefits paid	(186)	(153)
Impact of acquisitions (divestitures)	10	(9)
Actuarial loss	104	514
Settlements	(17)	(63)
Other, includes translation	(74)	49
Ending obligation	3,953	3,731	3,246
Change in fair value of plan assets:
Beginning fair value	2,926	2,642
Actual return on plan assets	222	279
Employer contribution	42	258
Benefits paid	(186)	(153)
Impact of acquisitions (divestitures)	7	(7)
Settlements	(17)	(63)
Other, includes translation	51	(30)
Ending fair value	3,045	2,926	$ 2,642
Funded Status at September 30:
Unfunded benefit obligation	(908)	(804)
Amounts recognized in the Consolidated Balance Sheets at September 30:
Other	16	11
Salaries, wages and related items	(23)	(22)
Long-term Employee Benefit Obligations	(901)	(793)
Net amount recognized	(908)	(804)
Amounts recognized in Accumulated other comprehensive income (loss) before income taxes at September 30:
Prior service credit	31	44
Net actuarial loss	(1,281)	(1,289)
Net amount recognized	$ (1,250)	$ (1,246)