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Financial Instruments - Schedule Of Available-For-Sale Investments With Unrealized Losses (Details) - USD ($)
$ in Millions
Dec. 31, 2023
Dec. 31, 2022
Schedule of Available-for-sale Securities [Line Items]    
Unrealized losses less than 12 months, fair value $ 132.5 $ 1,510.4
Unrealized losses less than 12 months (0.1) (49.1)
Unrealized losses 12 months or greater, fair value 2,595.1 3,538.3
Unrealized losses 12 months or greater (60.4) (149.4)
Total Fair Value 2,727.6 5,048.7
Total Unrealized Losses (60.5) (198.5)
U.S. treasuries    
Schedule of Available-for-sale Securities [Line Items]    
Unrealized losses less than 12 months, fair value 48.5 731.7
Unrealized losses less than 12 months 0.0 (26.0)
Unrealized losses 12 months or greater, fair value 1,112.9 1,886.9
Unrealized losses 12 months or greater (25.4) (70.6)
Total Fair Value 1,161.4 2,618.6
Total Unrealized Losses (25.4) (96.6)
Corporate debt securities    
Schedule of Available-for-sale Securities [Line Items]    
Unrealized losses less than 12 months, fair value 54.2 631.4
Unrealized losses less than 12 months (0.1) (17.6)
Unrealized losses 12 months or greater, fair value 1,219.2 1,221.9
Unrealized losses 12 months or greater (25.8) (58.4)
Total Fair Value 1,273.4 1,853.3
Total Unrealized Losses (25.9) (76.0)
U.S. government agencies    
Schedule of Available-for-sale Securities [Line Items]    
Unrealized losses less than 12 months, fair value 29.8 102.7
Unrealized losses less than 12 months 0.0 (4.4)
Unrealized losses 12 months or greater, fair value 185.6 324.6
Unrealized losses 12 months or greater (7.3) (15.5)
Total Fair Value 215.4 427.3
Total Unrealized Losses (7.3) (19.9)
Municipal securities    
Schedule of Available-for-sale Securities [Line Items]    
Unrealized losses less than 12 months, fair value 0.0 44.6
Unrealized losses less than 12 months 0.0 (1.1)
Unrealized losses 12 months or greater, fair value 77.4 104.9
Unrealized losses 12 months or greater (1.9) (4.9)
Total Fair Value 77.4 149.5
Total Unrealized Losses $ (1.9) $ (6.0)