Marketable Securities and Equity Investments - Narrative (Details) - USD ($)	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018	Dec. 31, 2018
Summary of cash, cash equivalents and marketable securities
Cash	$ 1,500,000,000		$ 1,400,000,000
Other-than-temporary declines in fair value of available-for-sale debt securities	0	$ 0
Gross realized gains or losses	0	0
Unrealized gains to other (expense) income, net	43,600,000	95,500,000
Payments to acquire investment	0	$ 21,500,000
Other assets
Summary of cash, cash equivalents and marketable securities
Equity securities without readily determinable fair value, amount	13,600,000
Corporate equity securities
Summary of cash, cash equivalents and marketable securities
Equity Securities, FV-NI	$ 210,874,000		$ 167,323,000