Condensed Consolidated Statements of Cash Flows (Unaudited) Reconciliation of cash, cash equivalents and restricted cash - USD ($) $ in Millions	Mar. 31, 2018	Dec. 31, 2017	Mar. 31, 2017	Dec. 31, 2016
Cash and Cash Equivalents [Abstract]
Cash and cash equivalents	$ 348	$ 537	$ 401
Restricted Cash	7		5
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents	$ 355	$ 543	$ 406	$ 507