Cash and Cash Equivalents and Restricted Cash and Cash Equivalents Supplmental Cash Flow Disclosures (Details) - USD ($) $ in Millions	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Condensed Cash Flow Statements, Captions [Line Items]
Cash and cash equivalents	$ 627	$ 935
Restricted Cash and Cash Equivalents, Current	227	327
Restricted Cash and Cash Equivalents, Noncurrent	29	21
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents	$ 883	$ 1,283	$ 1,003	$ 1,332