Segment Information - Foreign and U.S. Revenues (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenues from external customers	$ 11,102	$ 10,074	$ 33,314	$ 30,265