Retirement Plans (Details) $ in Millions	12 Months Ended
Sep. 30, 2017 USD ($) Person	Sep. 30, 2016 USD ($)	Sep. 30, 2015 USD ($)
Retirement Plans [Line Items]
Defined benefit plan, pension plans with accumulated benefit obligations in excess of plan assets, aggregate projected benefit obligation	$ 5,564	$ 7,124
Defined benefit plan, pension plans with accumulated benefit obligations in excess of plan assets, aggregate accumulated benefit obligation	5,465	6,966
Defined benefit plan, pension plans with accumulated benefit obligations in excess of plan assets, aggregate fair value of plan assets	4,715	5,234
Total employer and employee contributions to defined benefit plans	342
Voluntary contributions made by the company to defined benefit plans	49
Estimated future employer contributions to defined benefit plans in next fiscal year	$ 100
Modification in salaried plans to limit company's cost of future annual retiree medical benefits	150.00%
Projected prescription drug subsidy receipts per year over the next ten years	$ 2
Matching contributions charged to expense for defined contribution savings plans	$ 138	128	$ 123
Number of multiemployer benefit plans in which the Company participates \| Person	289
Employer contributions to multiemployer pension plans	$ 67	46	45
Postretirement Benefits
Retirement Plans [Line Items]
Defined Benefit Plan, Benefit Obligation	214	$ 242	$ 211
Total employer and employee contributions to defined benefit plans	5
Estimated future employer contributions to defined benefit plans in next fiscal year	$ 5

Defined benefit plan aggregate contributions.

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- Definition

Percentage of 1993 cost to which the Company's cost of future annual retiree medical benefits is limited based on modifications to certain salaried plans.

+ References

No definition available.

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Number of multiemployer benefit plans in which the Company participates.

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Retirement Plans [Line Items]

+ References

No definition available.

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- Definition

Voluntary contributions made by the company to defined benefit plans.

+ References

No definition available.

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- Definition

1) For defined benefit pension plans, the benefit obligation is the projected benefit obligation, which is the actuarial present value as of a date of all benefits attributed by the pension benefit formula to employee service rendered prior to that date. 2) For other postretirement defined benefit plans, the benefit obligation is the accumulated postretirement benefit obligation, which is the actuarial present value of benefits attributed to employee service rendered to a particular date.

+ 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 (a)
-URI http://asc.fasb.org/extlink&oid=65897934&loc=d3e1928-114920

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Glossary Projected Benefit Obligation
-URI http://asc.fasb.org/extlink&oid=6522206

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Glossary Accumulated Postretirement Benefit Obligation
-URI http://asc.fasb.org/extlink&oid=6503904

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- Definition

If aggregate disclosures are presented, the aggregate pension accumulated benefit obligation for pension plans with accumulated benefit obligations in excess of plan assets as of the measurement date of each statement of financial position presented.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
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-SubTopic 20
-Section 55
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-URI http://asc.fasb.org/extlink&oid=73719040&loc=d3e4179-114921

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If aggregate disclosures are presented, the aggregate fair value of plan assets for pension plans with accumulated benefit obligations in excess of plan assets as of the measurement date of each statement of financial position presented.

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If aggregate disclosures are presented, the aggregate projected benefit obligation for pension plans with accumulated benefit obligations in excess of plan assets as of the measurement date of each statement of financial position presented.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
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- Definition

Amount of employer's best estimate of contributions expected to be paid to the plan during the next fiscal year beginning after the date of the latest statement of financial position.

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- Definition

The amount of the cost recognized during the period for defined contribution plans.

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-Name Accounting Standards Codification
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Amount of contributions made to multiemployer plans by the employer. A multiemployer plan is a pension or postretirement benefit plan to which two or more unrelated employers contribute where assets contributed by one participating employer may be used to provide benefits to employees of other participating employers.

+ References

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Amount of the effect of the government subsidy for prescription drug benefits on the measurement of net periodic postretirement benefit cost. That effect includes (1) any amortization of the actuarial experience gain, (2) the reduction in current period service cost due to the subsidy, and (3) the resulting reduction in interest cost on the accumulated postretirement benefit obligation as a result of the subsidy.

+ References

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