Amount of gain (loss) from change in actuarial assumptions which (increases) decreases benefit obligation of defined benefit plan. Assumptions include, but are not limited to, interest, mortality, employee turnover, salary, and temporary deviation from substantive plan.

Name:	us-gaap_DefinedBenefitPlanActuarialGainLoss
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

Employee Benefit Plans - Narrative (Details)	1 Months Ended	12 Months Ended
Employee Benefit Plans - Narrative (Details)	Sep. 30, 2018 USD ($) participant	Sep. 30, 2019 USD ($) multiemployer_plan	Sep. 30, 2018 USD ($)	Sep. 30, 2017 USD ($)
Defined Benefit Plan Disclosure [Line Items]
Remeasurement loss		$ 69,000,000	$ 38,000,000	$ (68,000,000)
Contribution plan expense		$ 14,000,000	14,000,000	14,000,000
Number of multiemployer plans \| multiemployer_plan		2
Reserves for incentive plans	$ 19,000,000	$ 25,000,000	19,000,000
United States \| Fixed securities
Defined Benefit Plan Disclosure [Line Items]
Target asset allocations		75.00%
United States \| Equity securities
Defined Benefit Plan Disclosure [Line Items]
Target asset allocations		25.00%
Pension benefits
Defined Benefit Plan Disclosure [Line Items]
Remeasurement loss		$ 253,000,000	(95,000,000)
Accumulated benefit obligations	$ 2,087,000,000	2,287,000,000	2,087,000,000	2,381,000,000
Employer contributions		14,000,000	16,000,000
Pension benefits \| Qualified Plan
Defined Benefit Plan Disclosure [Line Items]
Number of participants electing to receive lump sum payment settlement \| participant	2,600
Lump sum payments	$ 134,000,000
Pension benefits \| United States \| Qualified Plan
Defined Benefit Plan Disclosure [Line Items]
Employer contributions		4,000,000
Expected future contribution		0
Pension benefits \| United States and Foreign \| Nonqualified Plan
Defined Benefit Plan Disclosure [Line Items]
Expected future contribution		14,000,000
Expected future contribution, non-cash portion		$ 5,000,000
Other postretirement benefits
Defined Benefit Plan Disclosure [Line Items]
Annual base year per capita costs, basis spread, up to		1.50%
Assumed pre-65 health care cost trend rate		6.90%
Ultimate pre-65 health care cost trend rate		4.20%
Remeasurement loss		$ 8,000,000	0
Accumulated benefit obligations	51,000,000	55,000,000	51,000,000	$ 57,000,000
Employer contributions		6,000,000	7,000,000
Other various benefit plans
Defined Benefit Plan Disclosure [Line Items]
Current postemployment benefits liability	1,000,000	1,000,000	1,000,000
Noncurrent postemployment benefits liability	$ 3,000,000	$ 3,000,000	$ 3,000,000