Stockholders' Equity - Effect of VE Territory Covered Losses Through Conversion Rate Adjustments (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	3 Months Ended
	Dec. 31, 2021	Dec. 31, 2020
Conversion of Stock [Line Items]
Recovery through conversion rate adjustment	$ 0	$ 0
Series B preferred stock
Conversion of Stock [Line Items]
Reduction in equivalent number of as-converted shares of class A common stock (in shares)	0	0
Effective price per share (in dollars per share)	$ 201.68	$ 209.89
Recovery through conversion rate adjustment	$ 26	$ 9
Series C preferred stock
Conversion of Stock [Line Items]
Reduction in equivalent number of as-converted shares of class A common stock (in shares)	0	0
Effective price per share (in dollars per share)	$ 201.68	$ 209.89
Recovery through conversion rate adjustment	$ 3	$ 6