Unaudited Quarterly Financial Information Unaudited Quarterly Financial Information (Details) - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2025	Sep. 30, 2024	Sep. 30, 2023
Quarterly Financial Information Disclosure [Abstract]
Operating expenses	$ 11,103	$ 10,086	$ 10,360
Operating income	2,569	2,228	1,694
Net income (loss)	$ 1,360	$ 1,135	$ 500