CONDENSED CONSOLIDATED STATEMENTS OF COMPREHENSIVE OPERATIONS - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Statement of Comprehensive Income [Abstract]
Net Income	$ 266	$ 256	$ 661	$ 700
Related to marketable securities:
Unrealized holding gain (loss) arising during the period	1	(2)	5	17
Reclassification of (gain) loss into Other—net nonoperating income (expense)	(1)	0	0	(1)
Income tax effect	0	0	(2)	(6)
Total	0	(2)	3	10
Related to employee benefit plans:
Reclassification of net pension expense into Wages and benefits	5	5	16	15
Income tax effect	(2)	(1)	(5)	(5)
Total	3	4	11	10
Related to interest rate derivative instruments:
Unrealized holding gain (loss) arising during the period	0	1	(2)	(6)
Reclassification of (gain) loss into Aircraft rent	2	1	4	4
Income tax effect	(1)	(1)	(1)	1
Total	1	1	1	(1)
Other Comprehensive Income	4	3	15	19
Comprehensive Income	$ 270	$ 259	$ 676	$ 719