Pension Benefit Obligations - Underlying assumptions (Details)	12 Months Ended
Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2019
United States
Weighted-average assumptions to determine benefit obligation:
Discount rate (as a percent)	2.46%	2.20%	2.92%
Weighted-average assumptions to determine net periodic benefit cost:
Discount rate (as a percent)	2.20%	2.92%	4.10%
Expected long-term rate of return on plan assets (as a percent)	6.80%	7.30%	7.00%
International
Weighted-average assumptions to determine benefit obligation:
Discount rate (as a percent)	1.98%	1.67%	1.81%
Salary increase rate (as a percent)	3.13%	2.68%	2.52%
Weighted-average assumptions to determine net periodic benefit cost:
Discount rate (as a percent)	1.67%	1.81%	2.91%
Salary increase rate (as a percent)	2.68%	2.52%	2.79%
Expected long-term rate of return on plan assets (as a percent)	3.95%	4.03%	4.43%

Weighted average rate for present value of future retirement benefits cash flows, used to determine benefit obligation of defined benefit plan.

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- Definition

Weighted average rate increase of compensation, used to determine benefit obligation of defined benefit plan. Plan includes, but is not limited to, pay-related defined benefit plan.

+ References

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- Definition

Weighted average rate for present value of future retirement benefits cash flows, used to determine net periodic benefit cost of defined benefit plan.

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- Definition

Weighted average rate of return on plan assets, reflecting average rate of earnings expected on existing plan assets and expected contributions, used to determine net periodic benefit cost of defined benefit plan.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
-SubTopic 20
-Section 50
-Paragraph 1
-Subparagraph (k)(3)
-URI http://asc.fasb.org/extlink&oid=118255775&loc=d3e1928-114920

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
-SubTopic 20
-Section 50
-Paragraph 8
-URI http://asc.fasb.org/extlink&oid=118255775&loc=d3e2919-114920

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- Definition

Weighted average rate of compensation increase used to determine net periodic benefit cost of defined benefit plan. Plan includes, but is not limited to, pay-related defined benefit plan.

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