Cash and Cash Equivalents and Restricted Cash and Cash Equivalents Supplemental Cash Flow Disclosure (Details) - USD ($) $ in Millions	Jun. 30, 2019	Dec. 31, 2018	Jun. 30, 2018	Dec. 31, 2017
Condensed Cash Flow Statements, Captions [Line Items]
Cash and cash equivalents	$ 1,265	$ 627
Restricted cash and cash equivalents	214	227
Restricted Cash and Cash Equivalents, Noncurrent	27	29
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents	$ 1,506	$ 883	$ 1,544	$ 1,283