Income Taxes (Summary of Tax Loss and Tax Credit Carryforwards) (Details) - USD ($) $ in Millions	Dec. 31, 2023	Dec. 31, 2022
Tax Credit Carryforward [Line Items]
Deferred tax asset on tax carryforwards	$ 48.4	$ 23.7
Valuation allowance on tax carryforwards	(46.4)	$ (19.3)
Total
Tax Credit Carryforward [Line Items]
Deferred tax asset on tax carryforwards	48.4
Valuation allowance on tax carryforwards	(46.4)
Net deferred tax asset on tax carryforwards	2.0
U.S. Federal Tax Credits
Tax Credit Carryforward [Line Items]
2024-2028	0.0
After 2028	10.6
Indefinite	0.0
Total tax carryforwards	10.6
Deferred tax asset on tax carryforwards	10.6
Valuation allowance on tax carryforwards	(10.6)
Net deferred tax asset on tax carryforwards	0.0
U.S. Federal Tax Losses
Tax Credit Carryforward [Line Items]
2024-2028	0.0
After 2028	0.6
Indefinite	0.0
Total tax carryforwards	0.6
Deferred tax asset on tax carryforwards	0.1
Valuation allowance on tax carryforwards	(0.1)
Net deferred tax asset on tax carryforwards	0.0
U.S. State Tax Credits
Tax Credit Carryforward [Line Items]
2024-2028	1.1
After 2028	0.3
Indefinite	0.0
Total tax carryforwards	1.4
Deferred tax asset on tax carryforwards	1.1
Valuation allowance on tax carryforwards	(1.1)
Net deferred tax asset on tax carryforwards	0.0
U.S. State Tax Losses
Tax Credit Carryforward [Line Items]
2024-2028	67.9
After 2028	535.4
Indefinite	4.6
Total tax carryforwards	607.9
Deferred tax asset on tax carryforwards	33.0
Valuation allowance on tax carryforwards	(31.6)
Net deferred tax asset on tax carryforwards	1.4
Non- U.S. Tax Losses
Tax Credit Carryforward [Line Items]
2024-2028	0.2
After 2028	0.3
Indefinite	15.2
Total tax carryforwards	15.7
Deferred tax asset on tax carryforwards	3.6
Valuation allowance on tax carryforwards	(3.0)
Net deferred tax asset on tax carryforwards	$ 0.6