Cash Equivalents and Investments - Maturities of Fixed Income Securities (Details) - USD ($) $ in Millions	Jun. 30, 2020	Dec. 31, 2019
Amortized Cost
Amortized Cost	$ 1,423.2	$ 1,633.1
Estimated Fair Value
Total	1,469.4	1,671.4
Fixed Income Securities
Amortized Cost
Due in less than one year	699.0
Due between one and five years	704.9
Amortized Cost	1,403.9	1,614.0
Estimated Fair Value
Due in less than one year	700.3
Due between one and five years	712.4
Total	$ 1,412.7	$ 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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