Condensed Consolidating Supplemental Guarantor Information Reconciliation of cash, cash equivalents and restricted cash (Details) - USD ($) $ in Millions	Mar. 31, 2018	Dec. 31, 2017	Mar. 31, 2017	Dec. 31, 2016
Cash and Cash Equivalents, at Carrying Value	$ 348	$ 537	$ 401
Restricted Cash	7		5
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents	355	543	406	$ 507
Non-Guarantor Subsidiaries
Cash and Cash Equivalents, at Carrying Value	316	429	361
Restricted Cash	7		5
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents	323	435	366	428
Guarantor Subsidiary
Cash and Cash Equivalents, at Carrying Value	11	11	13
Restricted Cash	0		0
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents	11	10	13	12
Parent Issuer
Cash and Cash Equivalents, at Carrying Value	21	97	27
Restricted Cash	0		0
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents	21	98	27	67
Eliminations
Cash and Cash Equivalents, at Carrying Value	0	0	0
Restricted Cash	0		0
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents	$ 0	$ 0	$ 0	$ 0