Goodwill and Intangible Assets - Change in Carrying Amount (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015
Goodwill [Roll Forward]
Goodwill beginning	$ 18,026	$ 17,981
Goodwill acquired	95	45
Effect of currency translation adjustment	1
Goodwill ending	$ 18,122	$ 18,026