CONDENSED CONSOLIDATED STATEMENTS OF COMPREHENSIVE OPERATIONS - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Statement of Comprehensive Income [Abstract]
Net Income	$ 217	$ 259	$ 414	$ 645
Related to marketable securities:
Unrealized holding gain (loss) arising during the period	(2)	1	(19)	5
Reclassification of (gain) loss into Other—net nonoperating income (expense)	2	(1)	5	0
Income tax effect	1	0	4	(2)
Total	1	0	(10)	3
Related to employee benefit plans:
Reclassification of net pension expense into Wages and benefits	7	5	21	16
Income tax effect	(2)	(2)	(5)	(5)
Total	5	3	16	11
Related to interest rate derivative instruments:
Unrealized holding gain (loss) arising during the period	0	0	8	(2)
Reclassification of (gain) loss into Aircraft rent	2	2	3	4
Income tax effect	(1)	(1)	(3)	(1)
Total	1	1	8	1
Other Comprehensive Income	7	4	14	15
Comprehensive Income	$ 224	$ 263	$ 428	$ 660