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Debt Securities - Gross Unrealized Losses and Fair Value Available-For-Sale Investments in Unrealized Loss Position (Details) - USD ($)
$ in Millions
Mar. 31, 2023
Dec. 31, 2022
Commercial paper    
Debt Securities, Available-for-sale [Line Items]    
Less Than 12 Months, Fair Value $ 49.5 $ 32.1
Less Than 12 Months, Unrealized Loss (0.1) (0.2)
12 Months or Longer, Fair Value 0.0 0.0
12 Months or Longer, Unrealized Loss 0.0 0.0
Total, Fair Value 49.5 32.1
Total, Unrealized Loss (0.1) (0.2)
Corporate debt securities    
Debt Securities, Available-for-sale [Line Items]    
Less Than 12 Months, Fair Value 125.4 199.5
Less Than 12 Months, Unrealized Loss (1.1) (1.9)
12 Months or Longer, Fair Value 307.5 299.1
12 Months or Longer, Unrealized Loss (4.5) (5.6)
Total, Fair Value 432.9 498.6
Total, Unrealized Loss (5.6) (7.5)
Securities of government-sponsored entities    
Debt Securities, Available-for-sale [Line Items]    
Less Than 12 Months, Fair Value 34.3 107.7
Less Than 12 Months, Unrealized Loss (0.2) (2.5)
12 Months or Longer, Fair Value 199.5 198.4
12 Months or Longer, Unrealized Loss (4.2) (4.5)
Total, Fair Value 233.8 306.1
Total, Unrealized Loss $ (4.4) $ (7.0)