Employee Benefit Plans - Schedule of Change in Benefit Obligations (Details) - USD ($) $ in Millions	12 Months Ended
Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2017
Change in benefit obligations
Actuarial loss (gain)	$ 69	$ 38	$ (68)
Amounts recognized in the Consolidated Balance Sheets
Noncurrent benefit liabilities	387	333
Pension benefits
Change in benefit obligations
Benefit obligations at beginning of period	2,087	2,381
Service cost	2	2	2
Interest cost	81	75	86
Benefits paid	(140)	(146)
Actuarial loss (gain)	253	(95)
Currency exchange rate changes	(2)	(3)
Transfers in	6	9
Settlements	0	(136)
Benefit obligations at end of period	2,287	2,087	2,381
Change in plan assets
Fair value of plan assets at beginning of period	1,792	2,081
Actual return on plan assets	273	(30)
Employer contributions	14	16
Benefits paid	(140)	(146)
Currency exchange rate changes	(2)	(3)
Settlements	0	(136)
Transfers in	6	10
Fair value of plan assets at end of period	1,943	1,792	2,081
Unfunded status of the plans as of September 30	344	295
Amounts recognized in the Consolidated Balance Sheets
Current benefit liabilities	9	10
Noncurrent benefit liabilities	335	285
Net amount recognized	344	295
Amounts recognized in accumulated other comprehensive income (loss)
Prior service cost (credit)	$ 1	$ 2
Weighted-average plan assumptions
Discount rate	3.10%	4.28%
Rate of compensation increase	3.06%	3.10%
Other postretirement benefits
Change in benefit obligations
Benefit obligations at beginning of period	$ 51	$ 57
Service cost	0	0	0
Interest cost	2	2	1
Benefits paid	(6)	(7)
Actuarial loss (gain)	8	0
Currency exchange rate changes	0	(1)
Transfers in	0	0
Settlements	0	0
Benefit obligations at end of period	55	51	57
Change in plan assets
Fair value of plan assets at beginning of period	0	0
Actual return on plan assets	0	0
Employer contributions	6	7
Benefits paid	(6)	(7)
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	55	51
Amounts recognized in the Consolidated Balance Sheets
Current benefit liabilities	6	6
Noncurrent benefit liabilities	49	45
Net amount recognized	55	51
Amounts recognized in accumulated other comprehensive income (loss)
Prior service cost (credit)	$ (45)	$ (56)
Weighted-average plan assumptions
Discount rate	2.95%	4.08%
Rate of compensation increase	0.00%	0.00%

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.