Accounting Principles and Practices - Schedule of Changes in Accounting Principle (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Operating income	$ 799	$ 335
Other income (expense)	$ (15)	(2)
As Reported
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Operating income		343
Other income (expense)		(10)
Accounting Standards Update 2017-07 | Adjustments
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Operating income		(8)
Other income (expense)		$ 8