Recently Issued Accounting Pronouncements (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Excess tax benefits recognized	$ 81	$ 0	$ 0
Net cash provided by operating activities	2,155	1,259	1,331
Net cash used in financing activities	500	(202)	(413)
Movement in restricted cash related to acquisition	3,561	(3,561)	0
New Accounting Pronouncement, Early Adoption, Effect
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Excess tax benefits recognized	81
Premium payment	63
Adjustments For ASU 2016-09 | New Accounting Pronouncement, Early Adoption, Effect
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Net cash provided by operating activities		67	39
Net cash used in financing activities		$ 67	$ 39
Adjustments For ASU 2016-15 | New Accounting Pronouncement, Early Adoption, Effect | Pro Forma [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Movement in restricted cash related to acquisition	$ 3,600