Basis of Presentation and Principles of Consolidation Basis of Presentation and Principles of Consolidation - Reconciliation of Cash, Cash Equivalents, and Restricted Cash (Details) - USD ($) $ in Millions	Sep. 30, 2017	Dec. 31, 2016	Sep. 30, 2016	Dec. 31, 2015
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Cash and cash equivalents	$ 1,515	$ 1,513
Restricted Cash and Cash Equivalents, Current	2,798	3,113
Restricted Cash and Cash Equivalents, Noncurrent	101	5
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents	$ 4,414	$ 4,631	$ 5,088	$ 1,394