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Employee Benefit Plans - Plan Assets (Details) - USD ($) $ in Millions | Sep. 30, 2019 | Sep. 30, 2018
--- | --- | ---
Defined Benefit Plan Disclosure [Line Items] |  |
Defined benefit plan, assets for plan benefits | $ 337 | $ 341
Fair Value, Inputs, Level 1 [Member] |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Defined benefit plan, assets for plan benefits | 5 | 6
Fair Value, Inputs, Level 2 [Member] |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Defined benefit plan, assets for plan benefits | 332 | 335
Fair Value, Inputs, Level 3 [Member] |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Defined benefit plan, assets for plan benefits | 0 | 0
Cash and Cash Equivalents [Member] |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Defined benefit plan, assets for plan benefits | 5 | 6
Cash and Cash Equivalents [Member] | Fair Value, Inputs, Level 1 [Member] |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Defined benefit plan, assets for plan benefits | 5 | 6
Cash and Cash Equivalents [Member] | Fair Value, Inputs, Level 2 [Member] |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Defined benefit plan, assets for plan benefits | 0 | 0
Cash and Cash Equivalents [Member] | Fair Value, Inputs, Level 3 [Member] |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Defined benefit plan, assets for plan benefits | 0 | 0
U.S. Government Securities [Member] |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Defined benefit plan, assets for plan benefits | 29 | 19
U.S. Government Securities [Member] | Fair Value, Inputs, Level 1 [Member] |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Defined benefit plan, assets for plan benefits | 0 | 0
U.S. Government Securities [Member] | Fair Value, Inputs, Level 2 [Member] |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Defined benefit plan, assets for plan benefits | 29 | 19
U.S. Government Securities [Member] | Fair Value, Inputs, Level 3 [Member] |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Defined benefit plan, assets for plan benefits | 0 | 0
Non-U.S. Government Securities [Member] |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Defined benefit plan, assets for plan benefits | 73 | 56
Non-U.S. Government Securities [Member] | Fair Value, Inputs, Level 1 [Member] |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Defined benefit plan, assets for plan benefits | 0 | 0
Non-U.S. Government Securities [Member] | Fair Value, Inputs, Level 2 [Member] |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Defined benefit plan, assets for plan benefits | 73 | 56
Non-U.S. Government Securities [Member] | Fair Value, Inputs, Level 3 [Member] |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Defined benefit plan, assets for plan benefits | 0 | 0
Corporate Debt Instruments [Member] |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Defined benefit plan, assets for plan benefits | 145 | 147
Corporate Debt Instruments [Member] | Fair Value, Inputs, Level 1 [Member] |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Defined benefit plan, assets for plan benefits | 0 | 0
Corporate Debt Instruments [Member] | Fair Value, Inputs, Level 2 [Member] |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Defined benefit plan, assets for plan benefits | 145 | 147
Corporate Debt Instruments [Member] | Fair Value, Inputs, Level 3 [Member] |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Defined benefit plan, assets for plan benefits | 0 | 0
Corporate Stocks [Member] |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Defined benefit plan, assets for plan benefits | 29 | 31
Corporate Stocks [Member] | Fair Value, Inputs, Level 1 [Member] |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Defined benefit plan, assets for plan benefits | 0 | 0
Corporate Stocks [Member] | Fair Value, Inputs, Level 2 [Member] |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Defined benefit plan, assets for plan benefits | 29 | 31
Corporate Stocks [Member] | Fair Value, Inputs, Level 3 [Member] |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Defined benefit plan, assets for plan benefits | 0 | 0
Listed Real Assets [Member] |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Defined benefit plan, assets for plan benefits | 11 | 10
Listed Real Assets [Member] | Fair Value, Inputs, Level 1 [Member] |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Defined benefit plan, assets for plan benefits | 0 | 0
Listed Real Assets [Member] | Fair Value, Inputs, Level 2 [Member] |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Defined benefit plan, assets for plan benefits | 11 | 10
Listed Real Assets [Member] | Fair Value, Inputs, Level 3 [Member] |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Defined benefit plan, assets for plan benefits | 0 | 0
Insurance Contracts [Member] |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Defined benefit plan, assets for plan benefits | 23 | 50
Insurance Contracts [Member] | Fair Value, Inputs, Level 1 [Member] |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Defined benefit plan, assets for plan benefits | 0 | 0
Insurance Contracts [Member] | Fair Value, Inputs, Level 2 [Member] |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Defined benefit plan, assets for plan benefits | 23 | 50
Insurance Contracts [Member] | Fair Value, Inputs, Level 3 [Member] |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Defined benefit plan, assets for plan benefits | 0 | 0
Accounts Receivable Securitization [Member] |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Defined benefit plan, assets for plan benefits | 22 | 22
Accounts Receivable Securitization [Member] | Fair Value, Inputs, Level 1 [Member] |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Defined benefit plan, assets for plan benefits | 0 | 0
Accounts Receivable Securitization [Member] | Fair Value, Inputs, Level 2 [Member] |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Defined benefit plan, assets for plan benefits | 22 | 22
Accounts Receivable Securitization [Member] | Fair Value, Inputs, Level 3 [Member] |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Defined benefit plan, assets for plan benefits | $ 0 | $ 0

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