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Cash, Cash Equivalents and Short-Term Investments - Unrealized Loss Position Aggregated By Investment (Details) - USD ($)
$ in Millions
Mar. 31, 2022
Dec. 31, 2021
Less than 12 months    
Fair Value $ 820.0 $ 941.0
Gross Unrealized Losses (25.8) (9.2)
More than 12 months    
Fair Value 117.0 0.0
Gross Unrealized Losses (7.2) 0.0
Total    
Fair Value 937.0 941.0
Gross Unrealized Losses (33.0) (9.2)
Corporate notes and obligations    
Less than 12 months    
Fair Value 444.2 498.6
Gross Unrealized Losses (13.5) (4.1)
More than 12 months    
Fair Value 28.9 0.0
Gross Unrealized Losses (2.1) 0.0
Total    
Fair Value 473.1 498.6
Gross Unrealized Losses (15.6) (4.1)
U.S. Treasury securities    
Less than 12 months    
Fair Value 173.7 218.0
Gross Unrealized Losses (5.3) (2.9)
More than 12 months    
Fair Value 62.1 0.0
Gross Unrealized Losses (3.9) 0.0
Total    
Fair Value 235.8 218.0
Gross Unrealized Losses (9.2) (2.9)
Asset backed securities    
Less than 12 months    
Fair Value 117.9 120.7
Gross Unrealized Losses (4.1) (1.2)
More than 12 months    
Fair Value 9.5 0.0
Gross Unrealized Losses (0.3) 0.0
Total    
Fair Value 127.4 120.7
Gross Unrealized Losses (4.4) (1.2)
Municipal securities    
Less than 12 months    
Fair Value 56.3 66.0
Gross Unrealized Losses (2.3) (0.7)
More than 12 months    
Fair Value 9.5 0.0
Gross Unrealized Losses (0.5) 0.0
Total    
Fair Value 65.8 66.0
Gross Unrealized Losses (2.8) (0.7)
U.S. agency obligations    
Less than 12 months    
Fair Value 10.5 14.4
Gross Unrealized Losses (0.3) (0.2)
More than 12 months    
Fair Value 3.5 0.0
Gross Unrealized Losses (0.2) 0.0
Total    
Fair Value 14.0 14.4
Gross Unrealized Losses (0.5) (0.2)
Foreign government obligations    
Less than 12 months    
Fair Value 11.3 15.4
Gross Unrealized Losses (0.2) 0.0
More than 12 months    
Fair Value 1.9 0.0
Gross Unrealized Losses (0.1) 0.0
Total    
Fair Value 13.2 15.4
Gross Unrealized Losses (0.3) 0.0
Supranational securities    
Less than 12 months    
Fair Value 6.1 7.9
Gross Unrealized Losses (0.1) (0.1)
More than 12 months    
Fair Value 1.6 0.0
Gross Unrealized Losses (0.1) 0.0
Total    
Fair Value 7.7 7.9
Gross Unrealized Losses $ (0.2) $ (0.1)