Cash and Cash Equivalents and Restricted Cash and Cash Equivalents Supplemental Cash Flow Disclosure (Details) - USD ($) $ in Millions	Sep. 30, 2019	Dec. 31, 2018	Sep. 30, 2018	Dec. 31, 2017
Condensed Cash Flow Statements, Captions [Line Items]
Cash and cash equivalents	$ 1,141	$ 627
Restricted cash and cash equivalents	238	227
Restricted Cash and Cash Equivalents, Noncurrent	27	29
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents	$ 1,406	$ 883	$ 1,402	$ 1,283