Accounting Policies - Reconciliation of Cash, Cash Equivalents, and Restricted Cash (Details) - USD ($) $ in Millions	Sep. 30, 2017	Dec. 31, 2016	Sep. 30, 2016	Dec. 31, 2015
Accounting Policies [Abstract]
Cash and Cash Equivalents	$ 822	$ 1,132	$ 975
Restricted Cash	46	57	25
Total Cash, Cash Equivalents and Restricted Cash	$ 868	$ 1,189	$ 1,000	$ 1,502