Other Financial Information (Intangibles) (Details) - USD ($) $ in Millions	Mar. 31, 2021	Sep. 30, 2020
Finite-Lived Intangible Assets [Line Items]
Gross carrying amount	$ 5,963	$ 5,106
Less: Accumulated amortization	2,868	2,638
Net carrying amount	3,095	2,468
Customer Relationships [Member]
Finite-Lived Intangible Assets [Line Items]
Net carrying amount	$ 1,597	$ 1,328

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

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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
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