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Benefit Plans Contributions (Details) - USD ($) | 12 Months Ended
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Sep. 30, 2019 | Sep. 30, 2018 | Sep. 30, 2017
Defined Benefit Plan Disclosure |  |  |  |
Employer contributions |  |  |  | $ 500,000,000
Other postretirement benefit contributions |  |  | $ 25,000,000 | 30,000,000
Contribution related to TVARS case |  |  | 15,000,000 | 20,000,000
Expected Payment for Postretirement Benefits |  |  | 29,000,000 |
Supplemental Employee Retirement Plans, Defined Benefit |  |  |  |
Defined Benefit Plan Disclosure |  |  |  |
Employer contributions |  |  |  | 5,000,000
Defined Benefit Plan, Expected Payments Related to SERP |  |  | 6,000,000 |
Defined Benefit Plan, Related to SERP |  |  | 4,000,000 |
Other Post-retirement Benefits |  |  |  |
Defined Benefit Plan Disclosure |  |  |  |
Employer contributions | [1] |  | 36,000,000 | 36,000,000
Pension Benefits |  |  |  |
Defined Benefit Plan Disclosure |  |  |  |
Employer contributions |  |  | 304,000,000 | 805,000,000
Other Pension Plans, Defined Benefit |  |  |  |
Defined Benefit Plan Disclosure |  |  |  |
Employer contributions |  |  | 300,000,000 | $ 800,000,000
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 |  |
[1] | Other Post-Retirement Benefits Employer contributions are reduced by provider discounts and rebates.

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- Definition Amount of contribution received by defined benefit plan from employer which increases plan assets. + References Reference 1: http://www.xbrl.org/2003/role/exampleRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 55 -Paragraph 17 -URI http://asc.fasb.org/extlink&oid=112275985&loc=d3e4179-114921 Reference 2: http://www.xbrl.org/2003/role/exampleRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (d)(iv)(01) -URI http://asc.fasb.org/extlink&oid=108410482&loc=d3e1928-114920 Reference 3: http://www.xbrl.org/2003/role/exampleRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (d)(ii) -URI http://asc.fasb.org/extlink&oid=108410482&loc=d3e1928-114920 Reference 4: http://www.xbrl.org/2009/role/commonPracticeRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 6 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=108410482&loc=d3e2709-114920 Reference 5: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (b)(3) -URI http://asc.fasb.org/extlink&oid=108410482&loc=d3e1928-114920 + Details
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