Fair Value Measurements and Investments - Additional Information (Detail) - USD ($)	Feb. 01, 2021	Mar. 31, 2021	Sep. 30, 2020
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
U.S. securities		$ 2,000,000,000.0	$ 3,800,000,000
Impairment of indefinite-lived intangible assets and goodwill	$ 0
Carrying value of long-term debt		$ 20,974,000,000	24,070,000,000
Minimum
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale investment securities, stated maturities		1 year
Maximum
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale investment securities, stated maturities		5 years
Senior Notes
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Carrying value of long-term debt		$ 21,000,000,000.0	24,100,000,000
Estimated Fair Value | Senior Notes
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Estimated fair value of long-term debt		$ 22,100,000,000	$ 26,600,000,000