Cash, Cash Equivalents and Short-Term Investments - Contractual Maturities (Details) - USD ($) $ in Millions	Jun. 30, 2020	Mar. 31, 2020
Amortized cost
Due within one year	$ 434.1
Due between one to three years	304.2
Due after three years	39.6
Total	$ 777.9
Estimated fair value
Due within one year		$ 435.7
Due between one to three years		307.9
Due after three years		39.9
Total		$ 783.5