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Benefit Plans Contributions (Details) - USD ($)	12 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2018
Defined Benefit Plan Disclosure
Defined contribution plan contribution amount	$ 88,000,000	$ 84,000,000	$ 80,000,000
Other postretirement benefit contributions		36,000,000	25,000,000
Contribution related to TVARS case		4,000,000	15,000,000
Expected Payment for Postretirement Benefits	29,000,000
Supplemental Employee Retirement Plans, Defined Benefit
Defined Benefit Plan Disclosure
Defined Benefit Plan, Expected Payments Related to SERP	5,000,000
Defined Benefit Plan, Related to SERP		7,000,000	4,000,000
Other Post-retirement Benefits
Defined Benefit Plan Disclosure
Employer contributions		36,000,000	36,000,000
Pension Benefits
Defined Benefit Plan Disclosure
Employer contributions		307,000,000	$ 304,000,000
Other Pension Plans, Defined Benefit
Defined Benefit Plan Disclosure
Employer contributions		300,000,000
Minimum | Other Pension Plans, Defined Benefit
Defined Benefit Plan Disclosure
Employer contributions		$ 300,000,000
Scenario, Forecast | Other Pension Plans, Defined Benefit
Defined Benefit Plan Disclosure
Employer contributions	$ 300,000,000

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