Income Taxes - Unrecognized Tax Benefits (Details) - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2022	Sep. 30, 2021	Sep. 30, 2020
Unrecognized Tax Benefits [Roll Forward]
Beginning balance	$ 499	$ 483	$ 414
Additions for tax positions related to the current year	62	29	96
Additions for tax positions of prior years	2	11	17
Reductions for tax positions of prior years	(52)	(9)	(38)
Settlements with taxing authorities	(3)	(12)	(4)
Statute closings	(9)	(3)	(2)
Ending balance	$ 499	$ 499	$ 483