CONSOLIDATED STATEMENTS OF COMPREHENSIVE OPERATIONS - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Net Income	$ 1,034	$ 814	$ 848
Related to marketable securities:
Unrealized holding gains (losses) arising during the period	(4)	1	(6)
Reclassification of (gains) losses into Other-net nonoperating income (expense)	1	(1)	1
Income tax benefit (expense)	1	0	2
Marketable securities, net of tax	(2)	0	(3)
Related to employee benefit plans:
Actuarial gains (losses) related to pension and other postretirement benefit plans	(123)	(43)	10
Reclassification of net pension expense into Wages and benefits	22	20	14
Income tax benefit (expense)	24	12	(14)
Employee benefit plans, net of tax	(77)	(11)	10
Related to interest rate derivative instruments:
Unrealized holding gains (losses) arising during the period	1	8	(5)
Reclassification of losses into Aircraft rent	5	6	6
Income tax benefit (expense)	(2)	(5)	(1)
Interest rate derivative instruments, net of tax	4	9	0
Other comprehensive income (loss)	(75)	(2)	7
Comprehensive income	$ 959	$ 812	$ 855