Retirement and Post-Retirement Employee Benefit Plans - Asset Allocation Postretirement Benefit Plan (Details) - Postretirement Plans	Sep. 30, 2020	Sep. 30, 2019
Diversified investment funds
Defined Benefit Plan Disclosure [Line Items]
Asset Allocation	97.40%	97.10%
Cash and cash equivalents
Defined Benefit Plan Disclosure [Line Items]
Asset Allocation	2.60%	2.90%

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.

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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Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant