Retirement Plans - Funded Status (Details) - Pension plan - USD ($) $ in Millions	12 Months Ended
Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2018
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Accumulated Benefit Obligation	$ 582	$ 571
Change in Projected Benefit Obligation:
Projected benefit obligation at beginning of year	598	547
Service cost	7	7	$ 8
Interest cost	10	13	14
Actuarial (gain) loss	16	96
Benefits paid	(22)	(40)
Settlements and curtailments	(11)	0
Divestitures	(12)	0
Currency translation adjustment	20	(25)
Projected benefit obligation at end of year	606	598	547
Change in Plan Assets:
Fair value of plan assets at beginning of year	470	449
Actual return on plan assets	12	63
Employer contributions/(distributions)	19	19
Benefits paid	(22)	(40)
Settlements and curtailments	(10)	0
Divestitures	(1)	0
Currency translation adjustment	18	(21)
Fair value of plan assets at end of year	486	470	$ 449
Funded status	(120)	(128)
Prepaid benefit cost
Change in Plan Assets:
Funded status	26	24
Accrued benefit liability
Change in Plan Assets:
Funded status	$ (146)	$ (152)

Defined Benefit Plan, Plan Assets, (Increase) Decrease for Settlement and Curtailment

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Amount of (increase) decrease in accumulated benefit obligation of defined benefit plan from effects of settlement and curtailment.

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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 funded (unfunded) status of defined benefit plan, measured as difference between fair value of plan assets and benefit obligation. Includes, but is not limited to, overfunded (underfunded) status.

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