Investments - Amortized Cost and Fair Values (Details) - USD ($) $ in Millions	Dec. 31, 2021	Dec. 31, 2020
Debt Securities, Available-for-sale [Line Items]
Cost or Amortized Cost	$ 696.8	$ 6.4
Gross unrealized gains	0.1	0.2
Gross unrealized losses	5.5	0.0
Debt securities, available-for-sale	691.4	6.6
Corporate debt securities
Debt Securities, Available-for-sale [Line Items]
Cost or Amortized Cost	593.4	0.0
Gross unrealized gains	0.0	0.0
Gross unrealized losses	4.7	0.0
Debt securities, available-for-sale	588.7	0.0
U.S. Government obligations
Debt Securities, Available-for-sale [Line Items]
Cost or Amortized Cost	102.2	6.4
Gross unrealized gains	0.1	0.2
Gross unrealized losses	0.8	0.0
Debt securities, available-for-sale	101.5	6.6
Municipal securities
Debt Securities, Available-for-sale [Line Items]
Cost or Amortized Cost	1.2	0.0
Gross unrealized gains	0.0	0.0
Gross unrealized losses	0.0	0.0
Debt securities, available-for-sale	$ 1.2	$ 0.0

Amount, before tax, of unrealized gain in accumulated other comprehensive income (AOCI) on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

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Amount, before tax, of unrealized loss in accumulated other comprehensive income (AOCI) on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

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Amortized cost of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
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Amount of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

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