RETIREMENT MEDICAL PLANS - Retiree Medical Plan Effect Of One Percentage Point Change In Assumed Health Care Cost Trend Rates (Details) - USD ($) $ in Millions	12 Months Ended
Sep. 30, 2017	Sep. 30, 2016
Retiree Medical Plan Effect Of One Percentage Point Change In Assumed Health Care Cost Trend Rates [Abstract]
Effect on total service and interest cost 1% increase	$ 0	$ 1
Effect on total service and interest cost 1% decrease	0	(1)
Effect on APBO 1% increase	5	40
Effect on APBO 1% decrease	$ (4)	$ (35)

Retiree Medical Plan Effect Of One Percentage Point Change In Assumed Health Care Cost Trend Rates.

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- Definition

Amount of decrease in accumulated postretirement benefit obligation from one-percentage-point decrease in assumed health care cost trend rate.

+ 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 (m)
-URI http://asc.fasb.org/extlink&oid=82843861&loc=d3e1928-114920

+ Details

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- Definition

Amount of decrease in service and interest cost components of net periodic postretirement benefit cost from one-percentage-point decrease in assumed health care cost trend rate.

+ References

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- Definition

Amount of increase in accumulated postretirement benefit obligation from one-percentage-point increase in assumed health care cost trend rate.

+ References

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- Definition

Amount of increase in service and interest cost components of net periodic postretirement benefit cost from one-percentage-point increase in assumed health care cost trend rate.

+ References

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