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Debt Securities - Amortized Cost, Gross Unrealized Gains and Losses, Allowance for Credit Losses and Fair Value of Debt Securities Available-For-Sale (Details) - USD ($)
$ in Millions
Jun. 30, 2023
Dec. 31, 2022
Debt Securities, Available-for-sale [Line Items]    
Amortized cost, current $ 821.1 $ 735.8
Unrealized gain, current 0.0 0.0
Unrealized loss, current (4.6) (9.4)
Fair value, current 816.5 726.4
Amortized cost, noncurrent 346.6 304.5
Unrealized gain, noncurrent 0.1 0.2
Unrealized loss, noncurrent (4.1) (5.3)
Fair value, noncurrent 342.6 299.4
Commercial paper    
Debt Securities, Available-for-sale [Line Items]    
Amortized cost, current 223.7 156.2
Unrealized gain, current 0.0 0.0
Unrealized loss, current 0.0 (0.2)
Fair value, current 223.7 156.0
Corporate debt securities    
Debt Securities, Available-for-sale [Line Items]    
Amortized cost, current 263.7 296.2
Unrealized gain, current 0.0 0.0
Unrealized loss, current (2.4) (3.2)
Fair value, current 261.3 293.0
Amortized cost, noncurrent 268.5 259.5
Unrealized gain, noncurrent 0.1 0.2
Unrealized loss, noncurrent (2.9) (4.3)
Fair value, noncurrent 265.7 255.4
Securities of government-sponsored entities    
Debt Securities, Available-for-sale [Line Items]    
Amortized cost, current 333.7 283.4
Unrealized gain, current 0.0 0.0
Unrealized loss, current (2.2) (6.0)
Fair value, current 331.5 277.4
Amortized cost, noncurrent 78.1 45.0
Unrealized gain, noncurrent 0.0 0.0
Unrealized loss, noncurrent (1.2) (1.0)
Fair value, noncurrent $ 76.9 $ 44.0