Stockholders' Equity - Effect of VE Territory Covered Losses Through Conversion Rate Adjustments (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	6 Months Ended
	Mar. 31, 2024	Mar. 31, 2023
Conversion of Stock [Line Items]
Recovery through conversion rate adjustment	$ 0	$ 1
Series B preferred stock
Conversion of Stock [Line Items]
Reduction in equivalent number of class A common stock (in shares)	0	0
Effective price per share (in dollars per share)	$ 254.32	$ 211.34
Recovery through conversion rate adjustment	$ 22	$ 7
Series C preferred stock
Conversion of Stock [Line Items]
Reduction in equivalent number of class A common stock (in shares)	0	0
Effective price per share (in dollars per share)	$ 254.32	$ 211.34
Recovery through conversion rate adjustment	$ 3	$ 7