Employee Retirement Plans - Net Periodic Pension Costs (Details) - Pension Benefits - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2019
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 12	$ 11	$ 10
Interest cost	22	23	27
Expected return on assets	(40)	(38)	(36)
Curtailment gain	0	(1)	0
Amortization of:
Prior service cost	0	1	0
Actuarial loss	14	15	8
Net cost	$ 8	$ 11	$ 9