CONDENSED CONSOLIDATED STATEMENTS OF COMPREHENSIVE OPERATIONS - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Statement of Comprehensive Income [Abstract]
Net Income (Loss)	$ 194	$ (431)	$ 460	$ (877)
Related to marketable securities:
Unrealized holding gain (loss) arising during the period	(4)	2	(15)	32
Reclassification of (gain) loss into Other - net nonoperating income (expense)	0	(2)	(6)	(11)
Income tax effect	1	0	5	(5)
Total	(3)	0	(16)	16
Related to employee benefit plans:
Reclassification of net pension expense into Wages and benefits and Other - net nonoperating income (expense)	8	7	25	22
Income tax effect	(2)	(1)	(6)	(5)
Total	6	6	19	17
Related to interest rate derivative instruments:
Unrealized holding gain (loss) arising during the period	2	2	11	(25)
Reclassification of loss into Aircraft rent	0	1	0	2
Income tax effect	0	(1)	(2)	5
Total	2	2	9	(18)
Other Comprehensive Income (Loss)	5	8	12	15
Comprehensive Income (Loss)	$ 199	$ (423)	$ 472	$ (862)