Employee Retirement Plans - Narrative (Details) - USD ($) $ in Millions	3 Months Ended	12 Months Ended
	Sep. 30, 2021	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2019
Defined Benefit Plan Disclosure [Line Items]
ABO	$ 31	$ 31	$ 24
Fair value of plan assets	19	19	17
Expected amortization of net actuarial losses	0	0
Pension Benefits
Defined Benefit Plan Disclosure [Line Items]
Expected amortization of net actuarial losses	7	7
Contribution made to Pension Plan		14	13
Projected benefit obligations of unfunded and non qualified supplemental executive retirement plans	870	870	782	$ 750
Costs associated with the plans		8	11	9
Net actuarial loss	13	13	24
Payments for defined benefit retirement plan		30	29
Supplemental Employee Retirement Plans
Defined Benefit Plan Disclosure [Line Items]
Projected benefit obligations of unfunded and non qualified supplemental executive retirement plans	57	57	59
Costs associated with the plans		0	0
Net actuarial loss	10	10	12
Payments for defined benefit retirement plan	12		0	0
Fair value of pension and other postretirement benefit contributions	$ 44	44	35
U.S. | Pension Benefits
Defined Benefit Plan Disclosure [Line Items]
Contribution made to Pension Plan		$ 13	$ 13	$ 12