CONDENSED CONSOLIDATED STATEMENTS OF COMPREHENSIVE OPERATIONS - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Statement of Comprehensive Income [Abstract]
Net Income (Loss)	$ (131)	$ (232)
Related to marketable securities:
Unrealized holding gain (loss) arising during the period	(11)	(1)
Reclassification of (gain) loss into Other - net nonoperating income (expense)	(4)	(3)
Income tax effect	3	1
Total	(12)	(3)
Related to employee benefit plans:
Reclassification of net pension expense into Wages and benefits and Other - net nonoperating income (expense)	(8)	(7)
Income tax effect	(2)	(2)
Total	6	5
Related to interest rate derivative instruments:
Unrealized holding gain (loss) arising during the period	(8)	(25)
Reclassification of loss into Aircraft rent	0	(1)
Income tax effect	(2)	(5)
Total	6	(19)
Other Comprehensive Income (Loss)	0	(17)
Comprehensive Income (Loss)	$ (131)	$ (249)