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Pension Benefit Obligations - Target Allocation and Plan Assets (Details)	Sep. 30, 2020	Sep. 30, 2019
United States
Components of net periodic benefit cost:
Target allocations (as a percent)	100.00%
Plan assets (as a percent)	100.00%	100.00%
United States | Equities
Components of net periodic benefit cost:
Target allocations (as a percent)	45.00%
Plan assets (as a percent)	47.00%	45.00%
United States | Debt.
Components of net periodic benefit cost:
Target allocations (as a percent)	43.00%
Plan assets (as a percent)	42.00%	44.00%
United States | Cash and cash equivalents
Components of net periodic benefit cost:
Target allocations (as a percent)	2.00%
Plan assets (as a percent)	1.00%	2.00%
United States | Property And Other
Components of net periodic benefit cost:
Target allocations (as a percent)	10.00%
Plan assets (as a percent)	10.00%	9.00%
International
Components of net periodic benefit cost:
Target allocations (as a percent)	100.00%
Plan assets (as a percent)	100.00%	100.00%
International | Equities
Components of net periodic benefit cost:
Target allocations (as a percent)	26.00%
Plan assets (as a percent)	26.00%	36.00%
International | Debt.
Components of net periodic benefit cost:
Target allocations (as a percent)	53.00%
Plan assets (as a percent)	54.00%	31.00%
International | Cash and cash equivalents
Components of net periodic benefit cost:
Target allocations (as a percent)	4.00%
Plan assets (as a percent)	4.00%	3.00%
International | Property And Other
Components of net periodic benefit cost:
Target allocations (as a percent)	17.00%
Plan assets (as a percent)	16.00%	30.00%

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Percentage of target investment allocation to total plan assets. Includes, but is not limited to, percentage on weighted-average basis if more than one plan.

+ References

Reference 1: http://www.xbrl.org/2003/role/exampleRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
-SubTopic 20
-Section 55
-Paragraph 17
-URI http://asc.fasb.org/extlink&oid=118257860&loc=d3e4179-114921

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
-SubTopic 20
-Section 50
-Paragraph 1
-Subparagraph (d)(i)
-URI http://asc.fasb.org/extlink&oid=118255775&loc=d3e1928-114920

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Percentage of actual investment allocation to total plan assets. Includes, but is not limited to, percentage on weighted-average basis if more than one plan.

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
-SubTopic 20
-Section 50
-Paragraph 1
-Subparagraph (d)(i)
-URI http://asc.fasb.org/extlink&oid=118255775&loc=d3e1928-114920

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