Fair Value Measurements and Investments - Additional Information (Detail) - USD ($) $ in Millions	3 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Sep. 30, 2021
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Debt securities due within one year	$ 2,300
Debt securities due within one to five years	2,100
Unrealized gain on equity securities held as of the end of the period	172	$ 29
Carrying value of long-term debt	20,920		$ 20,977
Senior Notes
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Carrying value of long-term debt	20,900		21,000
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	$ 22,500		$ 22,500