Retirement Plans (Details) $ in Millions	12 Months Ended
	Sep. 30, 2021 USD ($) Person	Sep. 30, 2020 USD ($)	Sep. 30, 2019 USD ($)
Retirement Plans [Line Items]
Matching contributions charged to expense for defined contribution savings plans	$ 118	$ 104	$ 198
Number of multiemployer benefit plans in which the Company participates | Person	275
Multiemployer Plan, Employer Contribution, Cost	$ 67	66	69
Pension Plan
Retirement Plans [Line Items]
Defined benefit plan, pension plans with accumulated benefit obligations in excess of plan assets, aggregate accumulated benefit obligation	4,402	5,539
Defined benefit plan, pension plans with accumulated benefit obligations in excess of plan assets, aggregate fair value of plan assets	3,841	4,528
Defined Benefit Plan, Pension Plan with Projected Benefit Obligation in Excess of Plan Assets, Projected Benefit Obligation	4,519	5,643
Defined Benefit Plan, Pension Plan with Projected Benefit Obligation in Excess of Plan Assets, Plan Assets	3,954	4,570
Postretirement Benefits
Retirement Plans [Line Items]
Defined Benefit Plan, Benefit Obligation	123	146	$ 174
Defined benefit plan, pension plans with accumulated benefit obligations in excess of plan assets, aggregate fair value of plan assets	38	34
Defined Benefit Plan, Pension Plan with Projected Benefit Obligation in Excess of Plan Assets, Projected Benefit Obligation	$ 96	$ 105