Employee Retirement Plans - Pension Plans (Details)	Sep. 30, 2017	Sep. 30, 2016
U.S. Pension Plan
Defined Benefit Plans and Other Postretirement Benefit Plans
Percentage of common stock represented pension plan assets	7.70%	8.00%
Pension Benefits \| U.S. Pension Plan
Defined Benefit Plans and Other Postretirement Benefit Plans
Actual	100.00%	100.00%
Target Asset Allocation	100.00%
Pension Benefits \| U.S. Pension Plan \| Equity investments
Defined Benefit Plans and Other Postretirement Benefit Plans
Actual	67.60%	64.30%
Target Asset Allocation	65.00%
Pension Benefits \| U.S. Pension Plan \| Equity investments \| Minimum
Defined Benefit Plans and Other Postretirement Benefit Plans
Target Asset Allocation	60.00%
Pension Benefits \| U.S. Pension Plan \| Equity investments \| Maximum
Defined Benefit Plans and Other Postretirement Benefit Plans
Target Asset Allocation	70.00%
Pension Benefits \| U.S. Pension Plan \| Domestic
Defined Benefit Plans and Other Postretirement Benefit Plans
Actual	55.20%	54.10%
Target Asset Allocation	52.50%
Pension Benefits \| U.S. Pension Plan \| Domestic \| Minimum
Defined Benefit Plans and Other Postretirement Benefit Plans
Target Asset Allocation	40.00%
Pension Benefits \| U.S. Pension Plan \| Domestic \| Maximum
Defined Benefit Plans and Other Postretirement Benefit Plans
Target Asset Allocation	65.00%
Pension Benefits \| U.S. Pension Plan \| International
Defined Benefit Plans and Other Postretirement Benefit Plans
Actual	12.40%	10.20%
Target Asset Allocation	12.50%
Pension Benefits \| U.S. Pension Plan \| International \| Minimum
Defined Benefit Plans and Other Postretirement Benefit Plans
Target Asset Allocation	7.50%
Pension Benefits \| U.S. Pension Plan \| International \| Maximum
Defined Benefit Plans and Other Postretirement Benefit Plans
Target Asset Allocation	17.50%
Pension Benefits \| U.S. Pension Plan \| Fixed income funds & cash equivalents
Defined Benefit Plans and Other Postretirement Benefit Plans
Actual	32.40%	35.70%
Target Asset Allocation	35.00%
Pension Benefits \| U.S. Pension Plan \| Fixed income funds & cash equivalents \| Minimum
Defined Benefit Plans and Other Postretirement Benefit Plans
Target Asset Allocation	30.00%
Pension Benefits \| U.S. Pension Plan \| 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 \| Domestic
Defined Benefit Plans and Other Postretirement Benefit Plans
Actual	63.10%	69.90%
Target Asset Allocation	65.00%
VEBA \| Domestic \| Minimum
Defined Benefit Plans and Other Postretirement Benefit Plans
Target Asset Allocation	60.00%
VEBA \| Domestic \| Maximum
Defined Benefit Plans and Other Postretirement Benefit Plans
Target Asset Allocation	70.00%
VEBA \| Fixed income funds & cash equivalents
Defined Benefit Plans and Other Postretirement Benefit Plans
Actual	36.90%	30.10%
Target Asset Allocation	35.00%
VEBA \| Fixed income funds & cash equivalents \| Minimum
Defined Benefit Plans and Other Postretirement Benefit Plans
Target Asset Allocation	30.00%
VEBA \| Fixed income funds & cash equivalents \| Maximum
Defined Benefit Plans and Other Postretirement Benefit Plans
Target Asset Allocation	40.00%

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/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
-SubTopic 20
-Section 50
-Paragraph 1
-Subparagraph (d)(5)(i)
-URI http://asc.fasb.org/extlink&oid=82843861&loc=d3e1928-114920

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- Definition

Percentage of fair value of investments (categorized by debt securities, equity securities, real estate and other plan assets) to the fair value of plan assets held.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
-SubTopic 20
-Section 50
-Paragraph 5
-Subparagraph (c)
-URI http://asc.fasb.org/extlink&oid=82843861&loc=d3e2446-114920

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
-SubTopic 20
-Section 50
-Paragraph 1
-Subparagraph (d)(1)
-URI http://asc.fasb.org/extlink&oid=82843861&loc=d3e1928-114920

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+ References

No definition available.

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