Cash and Marketable Securities - Components of Investments (Details) - USD ($) $ in Millions	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Cash and Cash Equivalents [Line Items]
Cash & Cash Equivalents	$ 54.8	$ 224.0	$ 94.8	$ 69.2
Restricted Cash	65.5	86.9
Restricted Marketable Securities	82.2	72.6
Total	202.5	383.5
Cash
Cash and Cash Equivalents [Line Items]
Cash & Cash Equivalents	54.8	224.0
Restricted Cash	65.5	86.9
Restricted Marketable Securities	0.0	0.0
Total	120.3	310.9
Equity securities
Cash and Cash Equivalents [Line Items]
Cash & Cash Equivalents	0.0	0.0
Restricted Cash	0.0	0.0
Restricted Marketable Securities	82.2	72.6
Total	$ 82.2	$ 72.6