Employee Retirement Plans - Pension Plans (Details)	12 Months Ended
Sep. 30, 2015	Sep. 30, 2014
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	66.40%	66.90%
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	56.20%	55.60%
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%	11.30%
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	33.60%	33.10%
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	67.40%	67.90%
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	32.60%	32.10%
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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- Definition

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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- 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=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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