Income Tax - Effective Tax Rate (Detail) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Mar. 31, 2025	Mar. 31, 2024	Mar. 31, 2025	Mar. 31, 2024
Income Tax Disclosure [Abstract]
(Provision) benefit for income taxes	$ (49)	$ (47)	$ (90)	$ (81)
Effective tax rate	32.00%	33.00%	30.00%	34.00%