Employee Benefit Plans - Schedule of Change in Benefit Obligations (Details) - USD ($) $ in Millions	12 Months Ended
Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2019
Change in benefit obligations
Benefit obligations at beginning of period	$ 2,300
Actuarial (gain) loss	(72)	$ (22)	$ 69
Benefit obligations at end of period	2,200	2,300
Amounts in the Consolidated Balance Sheets
Noncurrent benefit liabilities (c)	258	317
Pension benefits
Change in benefit obligations
Benefit obligations at beginning of period	2,321	2,287
Service cost	2	3	2
Interest cost	43	61	81
Benefits paid	(133)	(132)
Actuarial (gain) loss	(31)	107
Currency exchange rate changes	2	1
Transfers in	3	3
Settlements	(4)	(9)
Benefit obligations at end of period	2,203	2,321	2,287
Change in plan assets
Fair value of plan assets at beginning of period	2,045	1,943
Actual return on plan assets	128	218
Employer contributions	14	22
Benefits paid	(133)	(133)
Currency exchange rate changes	2	1
Settlements	(4)	(9)
Transfers in	3	3
Fair value of plan assets at end of period	2,055	2,045	1,943
Unfunded status of the plans as of September 30	148	276
Assets for Plan Benefits, Defined Benefit Plan	72	1
Amounts in the Consolidated Balance Sheets
Current benefit liabilities (b)	9	10
Noncurrent benefit liabilities (c)	211	267
Net liabilities recognized	220	277
Balance in Accumulated other comprehensive loss
Prior service cost (credit)	$ 1	$ 1
Weighted-average plan assumptions
Discount rate	2.70%	2.59%
Rate of compensation increase	3.00%	3.00%
Pension benefits \| Liability
Amounts in the Consolidated Balance Sheets
Net liabilities recognized	$ 148	$ 276
Other postretirement benefits
Change in benefit obligations
Benefit obligations at beginning of period	52	55
Service cost	0	0	0
Interest cost	1	1	2
Benefits paid	(5)	(6)
Actuarial (gain) loss	0	2
Currency exchange rate changes	1	0
Transfers in	0	0
Settlements	0	0
Benefit obligations at end of period	49	52	55
Change in plan assets
Fair value of plan assets at beginning of period	0	0
Actual return on plan assets	0	0
Employer contributions	5	6
Benefits paid	(5)	(6)
Currency exchange rate changes	0	0
Settlements	0	0
Transfers in	0	0
Fair value of plan assets at end of period	0	0	$ 0
Unfunded status of the plans as of September 30	49	52
Assets for Plan Benefits, Defined Benefit Plan	0	0
Amounts in the Consolidated Balance Sheets
Current benefit liabilities (b)	5	5
Noncurrent benefit liabilities (c)	44	47
Net liabilities recognized	49	52
Balance in Accumulated other comprehensive loss
Prior service cost (credit)	$ (21)	$ (33)
Weighted-average plan assumptions
Discount rate	2.67%	2.39%
Rate of compensation increase	0.00%	0.00%
Assumed pre-65 health care cost trend rate	6.40%	6.70%

Amount, after 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).

Name:	us-gaap_DefinedBenefitPlanAccumulatedOtherComprehensiveIncomeNetPriorServiceCostCreditAfterTax
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

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.