Basis of Presentation and Significant Accounting Policies - Cash, Cash Equivalents and Restricted Cash (Details) - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Other long-term assets
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Restricted cash, noncurrent	$ 10	$ 12	$ 52