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Retirement Benefit Plans - Asset Allocation Ranges of Defined Benefit Plan Investments (Details) | Sep. 30, 2021 | Sep. 30, 2020
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Asset Allocation Range provides flexibility for the Plan's investments |  |
Total percent of plan assets | 100.00% | 100.00%
U.S. equities |  |
Asset Allocation Range provides flexibility for the Plan's investments |  |
Total percent of plan assets | 53.00% | 51.00%
U.S. equities | Minimum |  |
Asset Allocation Range provides flexibility for the Plan's investments |  |
Asset allocations | 30.00% |
U.S. equities | Maximum |  |
Asset Allocation Range provides flexibility for the Plan's investments |  |
Asset allocations | 70.00% |
Non-U.S. equities |  |
Asset Allocation Range provides flexibility for the Plan's investments |  |
Total percent of plan assets | 8.00% | 8.00%
Non-U.S. equities | Minimum |  |
Asset Allocation Range provides flexibility for the Plan's investments |  |
Asset allocations | 0.00% |
Non-U.S. equities | Maximum |  |
Asset Allocation Range provides flexibility for the Plan's investments |  |
Asset allocations | 20.00% |
U.S. debt securities |  |
Asset Allocation Range provides flexibility for the Plan's investments |  |
Total percent of plan assets | 37.00% | 40.00%
U.S. debt securities | Minimum |  |
Asset Allocation Range provides flexibility for the Plan's investments |  |
Asset allocations | 20.00% |
U.S. debt securities | Maximum |  |
Asset Allocation Range provides flexibility for the Plan's investments |  |
Asset allocations | 70.00% |
Non-U.S. debt securities |  |
Asset Allocation Range provides flexibility for the Plan's investments |  |
Total percent of plan assets | 1.00% | 0.00%
Non-U.S. debt securities | Minimum |  |
Asset Allocation Range provides flexibility for the Plan's investments |  |
Asset allocations | 0.00% |
Non-U.S. debt securities | Maximum |  |
Asset Allocation Range provides flexibility for the Plan's investments |  |
Asset allocations | 10.00% |
Other securities |  |
Asset Allocation Range provides flexibility for the Plan's investments |  |
Total percent of plan assets | 1.00% | 1.00%
Other securities | Minimum |  |
Asset Allocation Range provides flexibility for the Plan's investments |  |
Asset allocations | 0.00% |
Other securities | Maximum |  |
Asset Allocation Range provides flexibility for the Plan's investments |  |
Asset allocations | 60.00% |

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- Definition 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=123450688&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=123447040&loc=d3e1928-114920 + Details
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