Cash Equivalents and Investments - Maturities of Fixed Income Securities (Details) - USD ($) $ in Millions	Sep. 30, 2020	Dec. 31, 2019
Amortized Cost
Amortized Cost	$ 1,582.0	$ 1,633.1
Estimated Fair Value
Total	1,627.8	1,671.4
Fixed Income Securities
Amortized Cost
Due in less than one year	849.0
Due between one and five years	713.7
Amortized Cost	1,562.7	1,614.0
Estimated Fair Value
Due in less than one year	850.7
Due between one and five years	720.4
Total	$ 1,571.1	$ 1,614.9

Amortized cost of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

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