Summary of Significant Accounting Policies - Reclassifications (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Net cash from operating activities	$ 4,635	$ 3,115	$ 3,131
Net cash from investing activities	(5,309)	(1,008)	(1,849)
Net cash from financing activities	(549)	(1,882)	104
Net Change in Cash and Cash Equivalents	$ (1,223)	225	1,386
Effect of Correction
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Net cash from operating activities		443	216
Net cash from investing activities		(326)	(211)
Net cash from financing activities		(117)	(5)
Net Change in Cash and Cash Equivalents		$ 0	$ 0