Stockholders' Equity - Share Repurchases in the Open Market (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	12 Months Ended
	Sep. 30, 2024	Sep. 30, 2023	Sep. 30, 2022
Class of Stock [Line Items]
Total cost	$ 16,958	$ 12,182	$ 11,589
Unsettled repurchases	$ 4,909	$ 5,015
Class A common stock
Class of Stock [Line Items]
Shares repurchased in the open market (in shares)	64	55	56
Average repurchase cost per share (in dollars per share)	$ 266.24	$ 222.27	$ 206.47
Total cost	$ 16,958	$ 12,182	$ 11,589
Unsettled repurchases	$ 90