Financial Instruments and Fair Value , Fair Value Measurements (Details) - USD ($) $ in Millions | Jun. 30, 2021 | Dec. 31, 2020 |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Fair Value | $ 1,480.5 | $ 893.8 |
Corporate debt securities [Member] | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Fair Value | 485.7 | 411.5 |
Commercial paper [Member] | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Fair Value | 658.2 | 185.4 |
U.S. government securities [Member] | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Fair Value | 148.8 | 184.9 |
Certificates of deposit and term deposits [Member] | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Fair Value | 187.8 | 112 |
Recurring Basis [Member] | Fair Value [Member] | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Total Assets, Fair Value Disclosure | 1,561.1 | 1,060.5 |
Recurring Basis [Member] | Fair Value [Member] | Level 1 [Member] | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Total Assets, Fair Value Disclosure | 229.4 | 337.6 |
Recurring Basis [Member] | Fair Value [Member] | Level 2 [Member] | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Total Assets, Fair Value Disclosure | 1,331.7 | 722.9 |
Recurring Basis [Member] | Fair Value [Member] | Level 3 [Member] | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Total Assets, Fair Value Disclosure | 0 | 0 |
Recurring Basis [Member] | Fair Value [Member] | Corporate debt securities [Member] | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Fair Value | 485.7 | 413.7 |
Recurring Basis [Member] | Fair Value [Member] | Corporate debt securities [Member] | Level 1 [Member] | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Fair Value | 0 | 0 |
Recurring Basis [Member] | Fair Value [Member] | Corporate debt securities [Member] | Level 2 [Member] | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Fair Value | 485.7 | 413.7 |
Recurring Basis [Member] | Fair Value [Member] | Corporate debt securities [Member] | Level 3 [Member] | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Fair Value | 0 | 0 |
Recurring Basis [Member] | Fair Value [Member] | Commercial paper [Member] | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Fair Value | 658.2 | 197.2 |
Recurring Basis [Member] | Fair Value [Member] | Commercial paper [Member] | Level 1 [Member] | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Fair Value | 0 | 0 |
Recurring Basis [Member] | Fair Value [Member] | Commercial paper [Member] | Level 2 [Member] | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Fair Value | 658.2 | 197.2 |
Recurring Basis [Member] | Fair Value [Member] | Commercial paper [Member] | Level 3 [Member] | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Fair Value | 0 | 0 |
Recurring Basis [Member] | Fair Value [Member] | U.S. government securities [Member] | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Fair Value | 148.8 | 184.9 |
Recurring Basis [Member] | Fair Value [Member] | U.S. government securities [Member] | Level 1 [Member] | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Fair Value | 148.8 | 184.9 |
Recurring Basis [Member] | Fair Value [Member] | U.S. government securities [Member] | Level 2 [Member] | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Fair Value | 0 | 0 |
Recurring Basis [Member] | Fair Value [Member] | U.S. government securities [Member] | Level 3 [Member] | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Fair Value | 0 | 0 |
Recurring Basis [Member] | Fair Value [Member] | Certificates of deposit and term deposits [Member] | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Fair Value | 187.8 | 112 |
Recurring Basis [Member] | Fair Value [Member] | Certificates of deposit and term deposits [Member] | Level 1 [Member] | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Fair Value | 0 | 0 |
Recurring Basis [Member] | Fair Value [Member] | Certificates of deposit and term deposits [Member] | Level 2 [Member] | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Fair Value | 187.8 | 112 |
Recurring Basis [Member] | Fair Value [Member] | Certificates of deposit and term deposits [Member] | Level 3 [Member] | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Fair Value | 0 | 0 |
Recurring Basis [Member] | Fair Value [Member] | Money market funds [Member] | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Fair Value | 80.6 | 152.7 |
Recurring Basis [Member] | Fair Value [Member] | Money market funds [Member] | Level 1 [Member] | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Fair Value | 80.6 | 152.7 |
Recurring Basis [Member] | Fair Value [Member] | Money market funds [Member] | Level 2 [Member] | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Fair Value | 0 | 0 |
Recurring Basis [Member] | Fair Value [Member] | Money market funds [Member] | Level 3 [Member] | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Fair Value | 0 | 0 |
Recurring Basis [Member] | Reported as [Member] | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Total Assets, Fair Value Disclosure | 1,561.1 | 1,060.5 |
Recurring Basis [Member] | Reported as [Member] | Cash equivalents [Member] | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Fair Value | 80.6 | 166.7 |
Recurring Basis [Member] | Reported as [Member] | Short-term investments [Member] | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Fair Value | 1,233.9 | 775.5 |
Recurring Basis [Member] | Reported as [Member] | Long-term investments [Member] | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Fair Value | $ 246.6 | $ 118.3 |