Summary of Significant Accounting Policies - Fair Value Measurements and Other Long-Term Investments (Details)	12 Months Ended
	Dec. 31, 2019 USD ($)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Variance threshold for outliers	$ 500,000
Variance threshold for outliers, percent	5.00%
Other long-term investments	$ 856,000,000
Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Other long-term investments	654,000,000
Fair Value Measured at Net Asset Value Per Share
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Other long-term investments	$ 202,000,000