Benefit Plans - Change in Benefit Obligation, Change in Fair Value of Plan Assets (Detail) - USD ($) $ in Millions	12 Months Ended
Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2017
Amounts recognized in the Consolidated Balance Sheets at September 30:
Long-term Employee Benefit Obligations	$ (1,272)	$ (1,056)
Pension Plans
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]
Beginning obligation	3,246	2,647
Service cost	134	136	$ 110
Interest cost	107	90	61
Plan amendments	(3)	0
Benefits paid	(153)	(162)
Impact of (divestitures) acquisitions	(9)	758
Actuarial loss (gain)	514	(82)
Settlements	(63)	(122)
Other, includes translation	49	19
Ending obligation	3,731	3,246	2,647
Change in fair value of plan assets:
Beginning fair value	2,642	1,932
Actual return on plan assets	279	70
Employer contribution	258	400
Benefits paid	(153)	(162)
Impact of (divestitures) acquisitions	(7)	539
Settlements	(63)	(122)
Other, includes translation	(30)	(15)
Ending fair value	2,926	2,642	$ 1,932
Funded Status at September 30:
Unfunded benefit obligation	(804)	(604)
Amounts recognized in the Consolidated Balance Sheets at September 30:
Other	11	15
Salaries, wages and related items	(22)	(15)
Long-term Employee Benefit Obligations	(793)	(604)
Net amount recognized	(804)	(604)
Amounts recognized in Accumulated other comprehensive income (loss) before income taxes at September 30:
Prior service credit	44	60
Net actuarial loss	(1,289)	(982)
Net amount recognized	$ (1,246)	$ (921)

Changes to benefit obligation which arose from business combination and/or divestiture transactions.

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Change to plan assets which arose from business combination and/or divestiture transactions.

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Amount, before tax, of accumulated other comprehensive (income) loss for defined benefit plan, that has not been recognized in net periodic benefit cost (credit).

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Amount, before tax, of accumulated other comprehensive income (loss) for gain (loss) of defined benefit plan, that has not been recognized in net periodic benefit (cost) credit.

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Amount, before tax, of accumulated other comprehensive (income) loss for cost (credit) of benefit change attributable to participants' prior service from plan amendment or plan initiation of defined benefit plan, that has not been recognized in net periodic benefit cost (credit).

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Amount of increase (decrease) in plan assets of defined benefit plan from actual return (loss) determined by change in fair value of plan assets adjusted for contributions, benefit payments, and other expenses.

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Amount of gain (loss) from change in actuarial assumptions which (increases) decreases benefit obligation of defined benefit plan. Assumptions include, but are not limited to, interest, mortality, employee turnover, salary, and temporary deviation from substantive plan.

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Amount of asset, recognized in statement of financial position, for overfunded defined benefit pension and other postretirement plans.

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A roll forward is a reconciliation of a concept from the beginning of a period to the end of a period.

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Amount of contribution received by defined benefit plan from employer which increases plan assets.

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Amount of asset segregated and restricted to provide benefit under defined benefit plan. Asset includes, but is not limited to, stock, bond, other investment, earning from investment, and contribution by employer and employee.

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Amount of liability, recognized in statement of financial position, for defined benefit pension and other postretirement plans, classified as current.

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