Fair Value Measurements and Investments - Additional Information (Detail) - USD ($)		3 Months Ended
	Feb. 01, 2020	Dec. 31, 2020	Dec. 31, 2019	Sep. 30, 2020
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
U.S. securities		$ 3,000,000,000.0		$ 3,800,000,000
Upward adjustments		14,000,000	$ 9,000,000
Downward adjustments		(2,000,000)
Impairment of indefinite-lived intangible assets and goodwill	$ 0
Impairment charges of non-marketable equity securities		0	$ 0
Carrying value of long-term debt		$ 21,055,000,000		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		$ 21,100,000,000		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		$ 23,800,000,000		$ 26,600,000,000