Fair Value Measurements and Investments - Additional Information (Detail) - USD ($)		3 Months Ended		6 Months Ended
	Feb. 01, 2025	Mar. 31, 2025	Mar. 31, 2024	Mar. 31, 2025	Mar. 31, 2024	Sep. 30, 2024
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Unrealized (loss) gain on investments		$ (23,000,000)	$ (23,000,000)	$ (33,000,000)	$ 13,000,000
Impairment of indefinite-lived intangible assets and goodwill	$ 0
Senior Notes
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Carrying value of debt		20,800,000,000		20,800,000,000		$ 20,800,000,000
Estimated Fair Value | Senior Notes
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Estimated fair value of debt		$ 18,700,000,000		$ 18,700,000,000		$ 19,200,000,000