Fair Value Measurements and Investments - Assets and Liabilities Measured (Details) - USD ($) $ in Millions	Sep. 30, 2019	Sep. 30, 2018
Assets
U.S. securities	$ 6,267	$ 7,516
Fair Value, Measurements, Recurring \| Level 1
Assets
Total	7,295	8,873
Liabilities
Deferred compensation liability	113	96
Total	113	96
Fair Value, Measurements, Recurring \| Level 2
Assets
Total	6,179	6,134
Liabilities
Total	52	22
Money market funds \| Fair Value, Measurements, Recurring \| Level 1
Assets
Cash equivalents and restricted cash equivalents:	6,494	6,252
U.S. government-sponsored debt securities \| Fair Value, Measurements, Recurring \| Level 2
Assets
Cash equivalents and restricted cash equivalents:	150	1,048
Equity securities \| Fair Value, Measurements, Recurring \| Level 1
Assets
Trading	126	113
U.S. government-sponsored debt securities
Assets
U.S. securities	5,592	5,008
U.S. government-sponsored debt securities \| Fair Value, Measurements, Recurring \| Level 2
Assets
U.S. securities	5,592	5,008
U.S. Treasury securities
Assets
U.S. securities	675	2,508
U.S. Treasury securities \| Fair Value, Measurements, Recurring \| Level 1
Assets
U.S. securities	675	2,508
Derivative instruments \| Fair Value, Measurements, Recurring \| Level 2
Assets
Derivative instruments	437	78
Liabilities
Derivative instruments	$ 52	$ 22

Fair value portion of accrued expenses.

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Fair value portion of probable future economic benefits obtained or controlled by an entity as a result of past transactions or events.

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Amount of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

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Fair value portion of currency on hand as well as demand deposits with banks or financial institutions. Includes other kinds of accounts that have the general characteristics of demand deposits. Also includes 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.

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Fair value of financial and nonfinancial obligations.

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Amount of investment in debt security measured at fair value with change in fair value recognized in net income (trading) and investment in equity security measured at fair value with change in fair value recognized in net income (FV-NI).

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