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	9 Months Ended
	Jun. 30, 2024	Jun. 30, 2025	Jun. 30, 2024
Conversion of Stock [Line Items]
Reduction in equivalent number of class A common stock (in shares)		1	0
Effective price per share (in dollars per share)		$ 346.79	$ 0
Deposits into the U.S. litigation escrow account		$ 375	$ 0
Recovery through conversion rate adjustment	$ (6)	$ 0	$ (6)
Series B preferred stock
Conversion of Stock [Line Items]
Reduction in equivalent number of class A common stock (in shares)		0	1
Effective price per share (in dollars per share)		$ 312.39	$ 270.07
Recovery through conversion rate adjustment		$ 5	$ 161
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)		$ 312.39	$ 269.62
Recovery through conversion rate adjustment		$ 3	$ 20