Legal Matters Legal Matters - Accrued Litigation (Details) - USD ($) $ in Millions	12 Months Ended	48 Months Ended
Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017
Loss Contingency Accrual [Roll Forward]
Accrued Litigation, Beginning of Period	$ 981	$ 1,024
Accrued Litigation, End of Period	982	981	$ 982
Unsettled
Loss Contingency Accrual [Roll Forward]
Provision for unsettled legal matters	19	2
Settled Litigation
Loss Contingency Accrual [Roll Forward]
Payments on unsettled and settled matters	(204)	(47)
U.S. Covered Litigation
Loss Contingency Accrual [Roll Forward]
Accrued Litigation, Beginning of Period	978	1,023
Accrued Litigation, End of Period	978	978	978
U.S. Covered Litigation \| Settled Litigation
Loss Contingency Accrual [Roll Forward]
Payments on unsettled and settled matters	0	(45)	(528)
VE Territory Covered Litigation
Loss Contingency Accrual [Roll Forward]
Accrued Litigation, Beginning of Period	2	0
Provision for unsettled legal matters	186	2
Accrued Litigation, End of Period	1	2	$ 1
VE Territory Covered Litigation \| Settled Litigation
Loss Contingency Accrual [Roll Forward]
Payments on unsettled and settled matters	$ (187)	$ 0

Amount of loss contingency liability.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 450
-SubTopic 20
-Section 50
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=82911808&loc=d3e14326-108349

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Amount of cash outflow reducing loss contingency liability.

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Amount charged against operating income increasing loss contingency liability, after adjustments to reduce previously estimated charges.

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