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Financial Derivative Instruments - Carrying Amount of Fair Value Hedges (Details) - USD ($) | Sep. 30, 2019 | Sep. 30, 2018
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Derivative [Line Items] |  |  |
Deferred Gain (Loss) on Discontinuation of Interest Rate Fair Value Hedge |  | $ 19,000,000 | $ 20,000,000
Designated as Hedging Instrument |  |  |
Derivative [Line Items] |  |  |
Derivative, Amount of Hedged Item |  | 801,000,000 | 783,000,000
Short-term Debt | Designated as Hedging Instrument |  |  |
Derivative [Line Items] |  |  |
Derivative, Amount of Hedged Item |  | 300,000,000 | 0
Long-term Debt | Designated as Hedging Instrument |  |  |
Derivative [Line Items] |  |  |
Derivative, Amount of Hedged Item |  | 501,000,000 | 783,000,000
Cumulative fair value adjustment [Member] | Designated as Hedging Instrument |  |  |
Derivative [Line Items] |  |  |
Derivative, Amount of Hedged Item | [1] | 20,000,000 | 3,000,000
Cumulative fair value adjustment [Member] | Short-term Debt | Designated as Hedging Instrument |  |  |
Derivative [Line Items] |  |  |
Derivative, Amount of Hedged Item | [1] | 2,000,000 | 0
Cumulative fair value adjustment [Member] | Long-term Debt | Designated as Hedging Instrument |  |  |
Derivative [Line Items] |  |  |
Derivative, Amount of Hedged Item | [1] | $ 18,000,000 | $ 3,000,000
[1] | At September 30, 2019 and 2018, these amounts include the cumulative amount of fair value hedging adjustments remaining for which hedge accounting has been discontinued of $19 million and $20 million, respectively.

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- Definition Amount as of the balance sheet date of the unamortized adjustment to the carrying value of an interest-bearing hedged item made under an effective interest rate fair value hedge that is amortized upon discontinuation of the interest rate fair value hedge. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 815 -SubTopic 25 -Section 35 -Paragraph 9 -URI http://asc.fasb.org/extlink&oid=118957181&loc=d3e75592-113984 + Details
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- Definition Amount of hedged item in hedging relationship. Excludes hedged asset or liability. + References No definition available. + Details
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- Definition Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table. + References No definition available. + Details
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- Details
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- Details
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- Details
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