Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalent (Details) - USD ($) $ in Millions	Dec. 31, 2018	Sep. 30, 2018	Dec. 31, 2017	Sep. 30, 2017
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents [Abstract]
Cash and cash equivalents	$ 8,289	$ 8,162	$ 8,138	$ 9,874
Escrow account	1,496	1,491	883	1,031
Customer collateral assets	1,330	1,324	1,155	1,106
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents	$ 11,115	$ 10,977	$ 10,176	$ 12,011

Amount of cash and cash equivalents restricted as to withdrawal or usage, classified as current. Cash includes, but is not limited to, currency on hand, demand deposits with banks or financial institutions, and other accounts with general characteristics of demand deposits. Cash equivalents include, but are not limited to, short-term, highly liquid investments that are both readily convertible to known amounts of cash and so near their maturity that they present insignificant risk of changes in value because of changes in interest rates.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
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Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
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Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant