New Accounting Standards (Details) - USD ($) $ in Millions		3 Months Ended		6 Months Ended
		Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Operating expenses	[1]	$ (5,213)	$ (4,590)	$ (9,914)	$ (9,176)
Selling, general and administrative expenses	[1]	$ (1,017)	$ (927)	$ (1,740)	(1,737)
Accounting Standards Update 2017-07
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Operating expenses					142
Selling, general and administrative expenses					$ 124

[1] 2017 adjusted to conform to ASU 2017-07. Refer to Note 5, "New Accounting Standards" beginning on page 10.