Accounting Policies - Reconciliation of Cash, Cash Equivalents, and Restricted Cash (Details) - USD ($) $ in Millions	Jun. 30, 2017	Dec. 31, 2016	Jun. 30, 2016	Dec. 31, 2015
Accounting Policies [Abstract]
Cash and Cash Equivalents	$ 903	$ 1,132	$ 1,138
Restricted Cash	66	57	15
Total Cash, Cash Equivalents and Restricted Cash	$ 969	$ 1,189	$ 1,153	$ 1,502