CONDENSED CONSOLIDATED STATEMENTS OF COMPREHENSIVE OPERATIONS - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Statement of Comprehensive Income [Abstract]
Net Income	$ 193	$ 293	$ 197	$ 386
Related to marketable securities:
Unrealized holding gain (loss) arising during the period	(4)	1	(17)	4
Reclassification of (gain) loss into Other—net nonoperating income (expense)	1	1	3	1
Income tax effect	0	(1)	3	(2)
Total	(3)	1	(11)	3
Related to employee benefit plans:
Reclassification of net pension expense into Wages and benefits	7	5	14	11
Income tax effect	(1)	(1)	(3)	(3)
Total	6	4	11	8
Related to interest rate derivative instruments:
Unrealized holding gain (loss) arising during the period	2	(3)	8	(2)
Reclassification of (gain) loss into Aircraft rent	0	2	1	2
Income tax effect	0	1	(2)	0
Total	2	0	7	0
Other Comprehensive Income	5	5	7	11
Comprehensive Income	$ 198	$ 298	$ 204	$ 397