Income Taxes - Schedule of Gross Unrecognized Tax Benefits (Details) - USD ($) $ in Millions	12 Months Ended
Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2017
Reconciliation of Unrecognized Tax Benefits, Excluding Amounts Pertaining to Examined Tax Returns [Roll Forward]
Unrecognized tax benefits, beginning of period	$ 10	$ 10	$ 8
Increases related to tax positions from prior years	5	2	0
Increases related to tax positions taken during the current year	0	1	2
Settlements with tax authorities	0	(2)	0
Lapses of statutes of limitation	(1)	(1)	0
Unrecognized tax benefits, end of period	14	10	$ 10
Accrual for tax interest and penalties	$ 2	$ 1

A roll forward is a reconciliation of a concept from the beginning of a period to the end of a period.

No definition available.

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- Definition

Amount of unrecognized tax benefits.

+ References

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- Definition

Amount of decrease in unrecognized tax benefits resulting from settlements with taxing authorities.

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- Definition

Amount accrued for interest on an underpayment of income taxes and penalties related to a tax position claimed or expected to be claimed in the tax return.

+ References

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Amount of increase in unrecognized tax benefits resulting from tax positions that have been or will be taken in current period tax return.

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Amount of increase in unrecognized tax benefits resulting from tax positions taken in prior period tax returns.

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Amount of decrease in unrecognized tax benefits resulting from lapses of applicable statutes of limitations.

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