Cash Flows Reclassification - Restricted Cash ASU 2016-18 (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
New Accounting Pronouncements and Changes in Accounting Principles [Abstract]
Excess Tax Benefit from Share-based Compensation, Operating Activities	$ 70	$ (14)	$ (81)
Adjustments for New Accounting Pronouncement [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Restricted cash	$ 2,500	2,900
Impact in restricted cash for operating activities		$ 358	$ (66)