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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
Mar. 31, 2023
Dec. 31, 2022
Debt Securities, Available-for-sale [Line Items]    
Amortized cost, current $ 798.0 $ 735.8
Unrealized gain, current 0.1 0.0
Unrealized loss, current (7.3) (9.4)
Fair value, current 790.8 726.4
Amortized cost, noncurrent 246.8 304.5
Unrealized gain, noncurrent 0.6 0.2
Unrealized loss, noncurrent (2.8) (5.3)
Fair value, noncurrent 244.6 299.4
Commercial paper    
Debt Securities, Available-for-sale [Line Items]    
Amortized cost, current 211.3 156.2
Unrealized gain, current 0.0 0.0
Unrealized loss, current (0.1) (0.2)
Fair value, current 211.2 156.0
Corporate debt securities    
Debt Securities, Available-for-sale [Line Items]    
Amortized cost, current 308.4 296.2
Unrealized gain, current 0.0 0.0
Unrealized loss, current (3.5) (3.2)
Fair value, current 304.9 293.0
Amortized cost, noncurrent 208.1 259.5
Unrealized gain, noncurrent 0.5 0.2
Unrealized loss, noncurrent (2.1) (4.3)
Fair value, noncurrent 206.5 255.4
Securities of government-sponsored entities    
Debt Securities, Available-for-sale [Line Items]    
Amortized cost, current 278.3 283.4
Unrealized gain, current 0.1 0.0
Unrealized loss, current (3.7) (6.0)
Fair value, current 274.7 277.4
Amortized cost, noncurrent 38.7 45.0
Unrealized gain, noncurrent 0.1 0.0
Unrealized loss, noncurrent (0.7) (1.0)
Fair value, noncurrent $ 38.1 $ 44.0