Employee Benefit Plans - Schedule of Level 3 Investments (Details) - Pension benefits - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2021	Sep. 30, 2020
Defined Benefit Plan, Change in Fair Value of Plan Assets, Level 3 Reconciliation [Roll Forward]
Fair value of plan assets at beginning of period	$ 2,045	$ 1,943
Fair value of plan assets at end of period	2,055	2,045
Level 3
Defined Benefit Plan, Change in Fair Value of Plan Assets, Level 3 Reconciliation [Roll Forward]
Fair value of plan assets at beginning of period	12	7
Purchases	48	4
Actual return on assets held at end of year	(2)	1
Fair value of plan assets at end of period	$ 58	$ 12