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Financial Derivative Instruments - Carrying Amount of Fair Value Hedges (Details) - USD ($)		Sep. 30, 2019	Sep. 30, 2018
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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Period Type:	instant

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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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