Stockholders' Equity - Effect of VE Territory Covered Losses Recovery on the Company Repurchasing its Common Stock (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	12 Months Ended
	Sep. 30, 2022	Sep. 30, 2021	Sep. 30, 2020
Conversion of Stock [Line Items]
Recovery through conversion rate adjustment	$ 0	$ (2)	$ 5
Series B
Conversion of Stock [Line Items]
Reduction in equivalent number of class A common stock (in shares)	8	0	16
Effective price per share (in dollars per share)	$ 197.93	$ 220.84	$ 194.31
Recovery through conversion rate adjustment	$ 135	$ 35	$ 72
Anniversary Releases	$ 1,510	$ 0	$ 3,084
Series C
Conversion of Stock [Line Items]
Reduction in equivalent number of class A common stock (in shares)	10	0	22
Effective price per share (in dollars per share)	$ 197.50	$ 220.71	$ 194.33
Recovery through conversion rate adjustment	$ 6	$ 20	$ 92
Anniversary Releases	$ 1,982	$ 0	$ 4,216