Fair Value Measurements and Investments - Additional Information (Detail) - USD ($)		3 Months Ended
	Feb. 01, 2019	Dec. 31, 2019	Dec. 31, 2018	Sep. 30, 2019
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value, Assets, Level 1 to Level 2 Transfers, Amount		$ 0
U.S. securities		5,500,000,000		$ 6,300,000,000
Upward adjustments		9,000,000
Downward adjustments		0
Impairment charges of non-marketable equity securities		$ 0	$ 0
Impairment of indefinite-lived intangible assets and goodwill	$ 0
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		$ 16,700,000,000		16,700,000,000
Estimated Fair Value | Senior Notes
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Estimated fair value of long-term deb		$ 18,300,000,000		$ 18,400,000,000