Fair Value Measurements and Investments - Assets and Liabilities Measured at Fair Value on a Recurring Basis (Details) - Recurring - USD ($) $ in Millions	Dec. 31, 2021	Sep. 30, 2021
Level 1
Assets
Total	$ 14,931	$ 17,658
Liabilities
Deferred compensation liability	209	167
Derivative instruments	0	0
Total	209	167
Level 1 | Money market funds
Assets
Cash equivalents and restricted cash equivalents	11,084	11,779
Other current and non-current assets	4	4
Level 1 | Marketable equity securities
Assets
Investment securities	481	490
Level 1 | U.S. government-sponsored debt securities
Assets
Cash equivalents and restricted cash equivalents	0	0
Investment securities	0	0
Level 1 | U.S. Treasury securities
Assets
Cash equivalents and restricted cash equivalents	1,075	2,400
Investment securities	2,287	2,985
Level 1 | Derivative instruments
Assets
Other current and non-current assets	0	0
Level 2
Assets
Total	1,459	755
Liabilities
Deferred compensation liability	0	0
Derivative instruments	62	109
Total	62	109
Level 2 | Money market funds
Assets
Cash equivalents and restricted cash equivalents	0	0
Other current and non-current assets	0	0
Level 2 | Marketable equity securities
Assets
Investment securities	0	0
Level 2 | U.S. government-sponsored debt securities
Assets
Cash equivalents and restricted cash equivalents	541	100
Investment securities	510	245
Level 2 | U.S. Treasury securities
Assets
Cash equivalents and restricted cash equivalents	0	0
Investment securities	0	0
Level 2 | Derivative instruments
Assets
Other current and non-current assets	$ 408	$ 410