Stockholders' Equity - Schedule of Effect of U.S. Retrospective Responsibility Plan on the Company Class Common B As-Converted Shares (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	12 Months Ended
	Sep. 30, 2025	Sep. 30, 2024	Sep. 30, 2023
Equity [Abstract]
Reduction in equivalent number of class A common stock (in shares)	3	5	5
Effective price per share (in dollars per share)	$ 343.41	$ 274.62	$ 221.33
Deposits into the U.S. litigation escrow account	$ 875	$ 1,500	$ 1,000