Condensed Consolidated Statements of Cash Flows Condensed Consolidated Statement of Cash Flows (Supplemental Disclosure) - USD ($) $ in Millions	Sep. 30, 2018	Dec. 31, 2017	Sep. 30, 2017	Dec. 31, 2016
Cash and cash equivalents	$ 168	$ 188	$ 210
Restricted cash and restricted cash equivalents included in Other current assets	781	803	453
Restricted cash equivalents included in Other long-term assets	31	26	27
Cash, cash equivalents, restricted cash and restricted cash equivalents at end of period	$ 980	$ 1,017	$ 690	$ 487