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Debt Securities - Gross Unrealized Losses and Fair Value Available-For-Sale Investments in Unrealized Loss Position (Details) - USD ($)
$ in Millions
Jun. 30, 2023
Dec. 31, 2022
Corporate debt securities    
Debt Securities, Available-for-sale [Line Items]    
Less Than 12 Months, Fair Value $ 248.0 $ 199.5
Less Than 12 Months, Unrealized Loss (2.4) (1.9)
12 Months or Longer, Fair Value 225.8 299.1
12 Months or Longer, Unrealized Loss (2.9) (5.6)
Total, Fair Value 473.8 498.6
Total, Unrealized Loss (5.3) (7.5)
Securities of government-sponsored entities    
Debt Securities, Available-for-sale [Line Items]    
Less Than 12 Months, Fair Value 262.8 107.7
Less Than 12 Months, Unrealized Loss (2.3) (2.5)
12 Months or Longer, Fair Value 76.3 198.4
12 Months or Longer, Unrealized Loss (1.1) (4.5)
Total, Fair Value 339.1 306.1
Total, Unrealized Loss $ (3.4) (7.0)
Commercial paper    
Debt Securities, Available-for-sale [Line Items]    
Less Than 12 Months, Fair Value   32.1
Less Than 12 Months, Unrealized Loss   (0.2)
12 Months or Longer, Fair Value   0.0
12 Months or Longer, Unrealized Loss   0.0
Total, Fair Value   32.1
Total, Unrealized Loss   $ (0.2)