Accounting Principles and Practices - Schedule of Changes in Accounting Principle (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Operating income	$ 262	$ 256	$ 1,045	$ 464
Other income (expense)	$ 1	4	$ (17)	6
As Reported
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Operating income		265		490
Other income (expense)		(5)		(20)
Adjustments | Accounting Standards Update 2017-07
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Operating income		(9)		(26)
Other income (expense)		$ 9		$ 26