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