Other Financial Information (Intangibles) (Details) - USD ($) $ in Millions	Mar. 31, 2020	Sep. 30, 2019
Finite-Lived Intangible Assets [Line Items]
Gross carrying amount	$ 4,916	$ 4,872
Less: Accumulated amortization	2,418	2,257
Net carrying amount	2,498	2,615
Customer Relationships [Member]
Finite-Lived Intangible Assets [Line Items]
Net carrying amount	$ 1,305	$ 1,391

Accumulated amount of amortization of assets, excluding financial assets and goodwill, lacking physical substance with a finite life.

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
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Amount before amortization of assets, excluding financial assets and goodwill, lacking physical substance with a finite life.

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Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
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Amount after amortization of assets, excluding financial assets and goodwill, lacking physical substance with a finite life.

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