Employee Retirement Plans - Pension Plans (Details)	12 Months Ended
Sep. 30, 2016	Sep. 30, 2015
Pension Benefit
Defined Benefit Plans and Other Postretirement Benefit Plans
Actual Pension Plan	100.00%	100.00%
Target Asset Allocation	100.00%
Pension Benefit \| Equity Securities
Defined Benefit Plans and Other Postretirement Benefit Plans
Actual Pension Plan	64.30%	66.40%
Target Asset Allocation	65.00%
Permitted Range - Minimum	60.00%
Permitted Range - Maximum	70.00%
Pension Benefit \| Domestic equity investments:
Defined Benefit Plans and Other Postretirement Benefit Plans
Actual Pension Plan	54.10%	56.20%
Target Asset Allocation	52.50%
Permitted Range - Minimum	40.00%
Permitted Range - Maximum	65.00%
Pension Benefit \| International Index Equity Mutual Funds
Defined Benefit Plans and Other Postretirement Benefit Plans
Actual Pension Plan	10.20%	10.20%
Target Asset Allocation	12.50%
Permitted Range - Minimum	7.50%
Permitted Range - Maximum	17.50%
Pension Benefit \| Fixed Income Funds and Cash Equivalents
Defined Benefit Plans and Other Postretirement Benefit Plans
Actual Pension Plan	35.70%	33.60%
Target Asset Allocation	35.00%
Permitted Range - Minimum	30.00%
Permitted Range - Maximum	40.00%
VEBA Trust
Defined Benefit Plans and Other Postretirement Benefit Plans
Actual Pension Plan	100.00%	100.00%
Target Asset Allocation	100.00%
VEBA Trust \| Domestic equity investments:
Defined Benefit Plans and Other Postretirement Benefit Plans
Actual Pension Plan	69.90%	67.40%
Target Asset Allocation	65.00%
Permitted Range - Minimum	60.00%
Permitted Range - Maximum	70.00%
VEBA Trust \| Fixed Income Funds and Cash Equivalents
Defined Benefit Plans and Other Postretirement Benefit Plans
Actual Pension Plan	30.10%	32.60%
Target Asset Allocation	35.00%
Permitted Range - Minimum	30.00%
Permitted Range - Maximum	40.00%

Target allocation of investments of this type to total plan assets presented on a weighted average basis.

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)(i)
-URI http://asc.fasb.org/extlink&oid=58740216&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)(i)
-URI http://asc.fasb.org/extlink&oid=58740216&loc=d3e1928-114920

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Target allocation maximum percentage of investments of this type to total plan assets presented on a weighted average basis.

+ References

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Target allocation minimum percentage of investments of this type to total plan assets presented on a weighted average basis.

+ 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)(i)
-URI http://asc.fasb.org/extlink&oid=58740216&loc=d3e1928-114920

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
-SubTopic 20
-Section 50
-Paragraph 5
-Subparagraph (c)(i)
-URI http://asc.fasb.org/extlink&oid=58740216&loc=d3e2446-114920

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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=58740216&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=58740216&loc=d3e1928-114920

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