Income Taxes - Schedule of Gross Unrecognized Tax Benefits (Details) - USD ($) $ in Millions	12 Months Ended
Sep. 30, 2025	Sep. 30, 2024	Sep. 30, 2023
Unrecognized Tax Benefits [Roll Forward]
Unrecognized tax benefits, beginning of period	$ 33.1	$ 35.7	$ 8.2
Increases related to tax positions from prior years	0.0	0.1	0.6
Decreases related to tax positions from prior years	0.0	(2.1)	(0.6)
Increases related to tax positions taken during the current year		0.0	27.7
Increases related to tax positions taken during the current year	0.0
Lapses of statutes of limitation	(0.3)	(0.6)	(0.2)
Unrecognized tax benefits, end of period	32.8	33.1	$ 35.7
Accrual for tax interest and penalties	$ 6.5	$ 1.8

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

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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.

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

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