Employee Retirement Plans - Pension Plans (Details)	Sep. 30, 2019	Sep. 30, 2018
Defined Benefit Plans and Other Postretirement Benefit Plans
Percentage of common stock represented pension plan assets	7.70%	8.50%
Pension Benefits \| U.S.
Defined Benefit Plans and Other Postretirement Benefit Plans
Actual	100.00%	100.00%
Target Asset Allocation	100.00%
Pension Benefits \| U.S. \| Total domestic equity investments
Defined Benefit Plans and Other Postretirement Benefit Plans
Actual	54.80%	58.20%
Target Asset Allocation	52.50%
Pension Benefits \| U.S. \| Total domestic equity investments \| Minimum
Defined Benefit Plans and Other Postretirement Benefit Plans
Target Asset Allocation	40.00%
Pension Benefits \| U.S. \| Total domestic equity investments \| Maximum
Defined Benefit Plans and Other Postretirement Benefit Plans
Target Asset Allocation	65.00%
Pension Benefits \| U.S. \| International index equity mutual funds
Defined Benefit Plans and Other Postretirement Benefit Plans
Actual	11.80%	11.80%
Target Asset Allocation	12.50%
Pension Benefits \| U.S. \| International index equity mutual funds \| Minimum
Defined Benefit Plans and Other Postretirement Benefit Plans
Target Asset Allocation	7.50%
Pension Benefits \| U.S. \| International index equity mutual funds \| Maximum
Defined Benefit Plans and Other Postretirement Benefit Plans
Target Asset Allocation	17.50%
Pension Benefits \| U.S. \| Equity investments
Defined Benefit Plans and Other Postretirement Benefit Plans
Actual	66.60%	70.00%
Target Asset Allocation	65.00%
Pension Benefits \| U.S. \| Equity investments \| Minimum
Defined Benefit Plans and Other Postretirement Benefit Plans
Target Asset Allocation	60.00%
Pension Benefits \| U.S. \| Equity investments \| Maximum
Defined Benefit Plans and Other Postretirement Benefit Plans
Target Asset Allocation	70.00%
Pension Benefits \| U.S. \| Fixed income funds & cash equivalents
Defined Benefit Plans and Other Postretirement Benefit Plans
Actual	33.40%	30.00%
Target Asset Allocation	35.00%
Pension Benefits \| U.S. \| Fixed income funds & cash equivalents \| Minimum
Defined Benefit Plans and Other Postretirement Benefit Plans
Target Asset Allocation	30.00%
Pension Benefits \| U.S. \| Fixed income funds & cash equivalents \| Maximum
Defined Benefit Plans and Other Postretirement Benefit Plans
Target Asset Allocation	40.00%
VEBA
Defined Benefit Plans and Other Postretirement Benefit Plans
Actual	100.00%	100.00%
Target Asset Allocation	100.00%
VEBA \| Total domestic equity investments
Defined Benefit Plans and Other Postretirement Benefit Plans
Actual	64.90%	65.60%
Target Asset Allocation	65.00%
VEBA \| Total domestic equity investments \| Minimum
Defined Benefit Plans and Other Postretirement Benefit Plans
Target Asset Allocation	60.00%
VEBA \| Total domestic equity investments \| Maximum
Defined Benefit Plans and Other Postretirement Benefit Plans
Target Asset Allocation	70.00%
VEBA \| Equity investments \| Minimum
Defined Benefit Plans and Other Postretirement Benefit Plans
Target Asset Allocation	30.00%
VEBA \| Equity investments \| Maximum
Defined Benefit Plans and Other Postretirement Benefit Plans
Target Asset Allocation	40.00%
VEBA \| Fixed income funds & cash equivalents
Defined Benefit Plans and Other Postretirement Benefit Plans
Actual	35.10%	34.40%
Target Asset Allocation	35.00%

Net costs for unfunded and non qualified supplemental executive retirement plans.

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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=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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- Definition

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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+ References

No definition available.

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