Retirement Plans (Details) $ in Millions	12 Months Ended
	Sep. 30, 2020 USD ($) Person	Sep. 30, 2019 USD ($)	Sep. 30, 2018 USD ($)
Retirement Plans [Line Items]
Defined benefit plan, pension plans with accumulated benefit obligations in excess of plan assets, aggregate projected benefit obligation	$ 5,598	$ 5,450
Defined benefit plan, pension plans with accumulated benefit obligations in excess of plan assets, aggregate accumulated benefit obligation	5,539	5,388
Defined benefit plan, pension plans with accumulated benefit obligations in excess of plan assets, aggregate fair value of plan assets	4,528	4,484
Total employer and employee contributions to defined benefit plans	58
Voluntary contributions made by the company to defined benefit plans	0
Estimated future employer contributions to defined benefit plans in next fiscal year	46
Projected prescription drug subsidy receipts per year over the next ten years	1
Matching contributions charged to expense for defined contribution savings plans	$ 104	198	$ 205
Number of multiemployer benefit plans in which the Company participates | Person	280
Multiemployer Plan, Employer Contribution, Cost	$ 66	69	68
Postretirement Benefits
Retirement Plans [Line Items]
Defined Benefit Plan, Benefit Obligation	146	$ 174	$ 196
Total employer and employee contributions to defined benefit plans	3
Estimated future employer contributions to defined benefit plans in next fiscal year	$ 3