Supplemental Financial Information - Cash, Cash Equivalents and Restricted Cash (Details) - USD ($) $ in Millions	Dec. 31, 2023	Sep. 30, 2023	Dec. 31, 2022	Sep. 30, 2022
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Cash and cash equivalents - continuing operations	$ 420.7	$ 409.1	$ 21.0
Total cash, cash equivalents and restricted cash	420.7	413.1	93.0	$ 83.9
Discontinued Operations, Held-for-sale
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Cash and cash equivalents - disposal group	0.0	4.0	0.0
Restricted cash - discontinued operations	0.0	0.0	1.5
Discontinued Operations, Disposed of by Sale
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Cash and cash equivalents - disposal group	$ 0.0	$ 0.0	$ 70.5