Debt Securities - Gross Unrealized Losses and Fair Value Available-For-Sale Investments in Unrealized Loss Position (Details) - USD ($) $ in Millions	Jun. 30, 2022	Dec. 31, 2021
Commercial paper
Debt Securities, Available-for-sale [Line Items]
Less Than 12 Months, Fair Value	$ 61.0
Less Than 12 Months, Unrealized Loss	(0.4)
12 Months or Longer, Fair Value	0.0
12 Months or Longer, Unrealized Loss	0.0
Total, Fair Value	61.0
Total, Unrealized Loss	(0.4)
Corporate debt securities
Debt Securities, Available-for-sale [Line Items]
Less Than 12 Months, Fair Value	403.8	$ 428.6
Less Than 12 Months, Unrealized Loss	(7.5)	(1.6)
12 Months or Longer, Fair Value	60.8	0.0
12 Months or Longer, Unrealized Loss	(0.8)	0.0
Total, Fair Value	464.6	428.6
Total, Unrealized Loss	(8.3)	(1.6)
Securities of government-sponsored entities
Debt Securities, Available-for-sale [Line Items]
Less Than 12 Months, Fair Value	329.1	230.5
Less Than 12 Months, Unrealized Loss	(7.4)	(1.0)
12 Months or Longer, Fair Value	11.5	0.0
12 Months or Longer, Unrealized Loss	(0.5)	0.0
Total, Fair Value	340.6	230.5
Total, Unrealized Loss	$ (7.9)	$ (1.0)

Amount of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale), in continuous unrealized loss position for more than 12 months, without allowance for credit loss. Includes beneficial interest in securitized financial asset.

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Amount of accumulated unrealized loss on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale), in continuous unrealized loss position for 12 months or longer, without allowance for credit loss. Includes beneficial interest in securitized financial asset.

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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), in continuous unrealized loss position for less than 12 months, without allowance for credit loss. Includes beneficial interest in securitized financial asset.

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