Basis of Presentation and Accounting Policies - Research and Development Expenses, and Earnings Per Share (Narrative) (Details) - USD ($) shares in Millions, $ in Millions	12 Months Ended
	Sep. 30, 2025	Sep. 30, 2024	Sep. 30, 2023
Accounting Policies [Abstract]
Research and development costs	$ 679	$ 658	$ 706
Antidilutive share-based compensation awards (in shares)	0.5	0.5	0.4