Equity and Noncontrolling Interests - Redeemable Noncontrolling Interest (Details) - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2025	Sep. 30, 2024	Sep. 30, 2023
Stockholders' Equity Attributable to Noncontrolling Interest [Roll Forward]
Beginning balance	$ 309
Dividends	(46)	$ (60)	$ (45)
Ending balance	297	309
Restatement adjustment
Stockholders' Equity Attributable to Noncontrolling Interest [Roll Forward]
Net income		5
Redeemable noncontrolling interest
Stockholders' Equity Attributable to Noncontrolling Interest [Roll Forward]
Beginning balance	91	57	45
Net income	36	38	27
Dividends	(31)	(21)	(18)
Foreign currency translation adjustments	(1)	17	3
Ending balance	$ 95	$ 91	$ 57