Cash, Cash Equivalents and Restricted Cash (Details) - USD ($) $ in Millions	Sep. 30, 2019	Dec. 31, 2018	Sep. 30, 2018	Dec. 31, 2017
Restricted Cash [Abstract]
Cash and cash equivalents	$ 339	$ 607
Restricted cash included in prepaid expenses and other current assets	53	45
Restricted cash included in other non-current assets	6	7
Total restricted cash	59	52
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents	$ 398	$ 659	$ 354	$ 435