Segment Information - Foreign and U.S. Revenues (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenues from external customers	$ 11,128	$ 10,066	$ 22,212	$ 20,191