Income Taxes - Income Before Income Taxes (Detail) - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2025	Sep. 30, 2024	Sep. 30, 2023
Income (Loss) from Continuing Operations before Equity Method Investments, Income Taxes, Noncontrolling Interest [Abstract]
Domestic	$ 15	$ 18	$ 65
Foreign	550	511	386
Income (loss) from operations before income taxes and equity in earnings of affiliated companies	$ 565	$ 529	$ 451