Cash and Cash Equivalents (Details) - USD ($) $ in Millions	Jun. 30, 2020	Dec. 31, 2019
Cash and Cash Equivalents [Line Items]
Total cash and cash equivalents	$ 779.1	$ 213.7
Cash
Cash and Cash Equivalents [Line Items]
Total cash and cash equivalents	470.3	85.3
Money market mutual funds
Cash and Cash Equivalents [Line Items]
Total cash and cash equivalents	305.9	115.5
Commercial Paper
Cash and Cash Equivalents [Line Items]
Total cash and cash equivalents	0.0	10.0
Restricted cash
Cash and Cash Equivalents [Line Items]
Total cash and cash equivalents	2.9	2.9
Level 1
Cash and Cash Equivalents [Line Items]
Total cash and cash equivalents	779.1	203.7
Level 1 | Cash
Cash and Cash Equivalents [Line Items]
Total cash and cash equivalents	470.3	85.3
Level 1 | Money market mutual funds
Cash and Cash Equivalents [Line Items]
Total cash and cash equivalents	305.9	115.5
Level 1 | Commercial Paper
Cash and Cash Equivalents [Line Items]
Total cash and cash equivalents	0.0	0.0
Level 1 | Restricted cash
Cash and Cash Equivalents [Line Items]
Total cash and cash equivalents	2.9	2.9
Level 2
Cash and Cash Equivalents [Line Items]
Total cash and cash equivalents	0.0	10.0
Level 2 | Cash
Cash and Cash Equivalents [Line Items]
Total cash and cash equivalents	0.0	0.0
Level 2 | Money market mutual funds
Cash and Cash Equivalents [Line Items]
Total cash and cash equivalents	0.0	0.0
Level 2 | Commercial Paper
Cash and Cash Equivalents [Line Items]
Total cash and cash equivalents	0.0	10.0
Level 2 | Restricted cash
Cash and Cash Equivalents [Line Items]
Total cash and cash equivalents	$ 0.0	$ 0.0