Income Taxes - Schedule of Tax Attributes and Valuation Allowances (Details) - USD ($) $ in Millions	Sep. 30, 2021	Sep. 30, 2020
Tax Benefit Amount
Non-United States capital loss carryforward	$ 15.3	$ 10.8
Net operating loss carryforwards	130.4	31.1
State tax credit carryforward	20.3	$ 17.3
Subtotal	166.0
Other deferred tax assets	5.5
Total	171.5
Valuation Allowance
Tax credit carryforward	5.5
Subtotal	27.1
Total	32.6
Non-United States
Tax Benefit Amount
Net operating loss carryforward, subject to expiration	6.6
Net operating loss carryforward, not subject to expiration	36.5
Non-United States capital loss carryforward	15.3
Valuation Allowance
Net operating loss carryforward, subject to expiration	6.2
Net operating loss carryforward, not subject to expiration	3.2
Non-United States capital loss carryforward	15.3
United States
Tax Benefit Amount
Net operating loss carryforward, subject to expiration	19.4
Net operating loss carryforward, not subject to expiration	50.7
State tax credit carryforward	9.4
Valuation Allowance
Net operating loss carryforward, subject to expiration	0.0
Net operating loss carryforward, not subject to expiration	0.0
Tax credit carryforward	1.2
State and Local
Tax Benefit Amount
Net operating loss carryforwards	17.2
State tax credit carryforward	10.9
Valuation Allowance
Net operating loss carryforward, subject to expiration	1.2
Tax credit carryforward	$ 0.0