Marketable Securities and Equity Investments - Additional Information (Details) - USD ($) |
12 Months Ended | ||
|---|---|---|---|
Dec. 31, 2019 |
Dec. 31, 2018 |
Dec. 31, 2017 |
|
| Summary of cash, cash equivalents and marketable securities | |||
| Cash | $ 2,300,000,000 | $ 1,400,000,000 | |
| Other-than-temporary declines in fair value of available-for-sale debt securities | 0 | 0 | $ 0 |
| Gross realized gains or losses | 0 | 0 | $ 0 |
| Unrealized gains to other (expense) income, net | 132,500,000 | 2,600,000 | |
| CRISPR Therapeutics | |||
| Summary of cash, cash equivalents and marketable securities | |||
| Marketable securities, fair value, investment in common stock | 282,100,000 | $ 167,300,000 | |
| Realized investment gains (losses) | 65,100,000 | ||
| Other assets | |||
| Summary of cash, cash equivalents and marketable securities | |||
| Equity securities without readily determinable fair value, amount | $ 40,800,000 | ||