Employee Benefit Plans - Narrative (Details)	12 Months Ended
	Sep. 30, 2021 USD ($) multiemployer_plan	Sep. 30, 2020 USD ($)	Sep. 30, 2019 USD ($)
Defined Benefit Plan Disclosure [Line Items]
Accumulated benefit obligations	$ 2,200,000,000	$ 2,300,000,000
Remeasurement (gain) loss	(72,000,000)	(22,000,000)	$ 69,000,000
Contribution plan expense	$ 19,000,000	15,000,000	14,000,000
Number of multiemployer plans | multiemployer_plan	2
Reserves for incentive plans	$ 49,000,000	39,000,000
United States | Fixed securities
Defined Benefit Plan Disclosure [Line Items]
Target asset allocations	83.00%
United States | Equity securities
Defined Benefit Plan Disclosure [Line Items]
Target asset allocations	17.00%
Pension benefits
Defined Benefit Plan Disclosure [Line Items]
Accumulated benefit obligations	$ 2,203,000,000	2,321,000,000	2,287,000,000
Remeasurement (gain) loss	(31,000,000)	107,000,000
Employer contributions	14,000,000	22,000,000
Expected future contribution	12,000,000
Pension benefits | United States | Qualified Plan
Defined Benefit Plan Disclosure [Line Items]
Expected future contribution	$ 0
Other postretirement benefits
Defined Benefit Plan Disclosure [Line Items]
Ultimate pre-65 health care cost trend rate	4.00%
Accumulated benefit obligations	$ 49,000,000	52,000,000	$ 55,000,000
Remeasurement (gain) loss	0	2,000,000
Employer contributions	5,000,000	6,000,000
Other various benefit plans
Defined Benefit Plan Disclosure [Line Items]
Noncurrent postemployment benefits liability	$ 3,000,000	$ 3,000,000