CONDENSED CONSOLIDATED STATEMENTS OF COMPREHENSIVE OPERATIONS - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Statement of Comprehensive Income [Abstract]
Net Income	$ 296	$ 260	$ 395	$ 444
Related to marketable securities:
Unrealized holding gains arising during the period	1	7	4	19
Reclassification of (gains) losses into Other—net nonoperating income (expense)	1	(1)	1	(1)
Income tax effect	(1)	(2)	(2)	(6)
Total	1	4	3	12
Related to employee benefit plans:
Reclassification of net pension expense into Wages and benefits	5	5	11	10
Income tax effect	(1)	(2)	(3)	(4)
Total	4	3	8	6
Related to interest rate derivative instruments:
Unrealized holding losses arising during the period	(3)	(2)	(2)	(7)
Reclassification of losses into Aircraft rent	2	2	2	3
Income tax effect	1	0	0	2
Total	0	0	0	(2)
Other Comprehensive Income	5	7	11	16
Comprehensive Income	$ 301	$ 267	$ 406	$ 460