Basis of Presentation and Summary of Significant Accounting Policies - Impact of Adoption - ASU 2017-07 (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Operating income (Loss)	$ 701	$ (284)	$ 457
Other non operating income, net	$ 202	80	3
Accounting Standards Update 2017-07
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Operating income (Loss)		(1)	24
Other non operating income, net		$ 1	$ (24)