Consolidated Statement of Comprehensive Income (Loss) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Net income (loss)	$ (3,074)	$ 2,300	$ 2,465
Unrealized gain (loss) on defined benefit plan items, net of deferred taxes of ($15), ($9), and $15	(48)	(29)	52
Other, net of deferred taxes of $7, $8, and ($2)	25	26	(6)
OTHER COMPREHENSIVE INCOME (LOSS)	(44)	(81)	26
COMPREHENSIVE INCOME (LOSS)	(3,118)	2,219	2,491
Operating Revenue	9,048	22,428	21,965
Supplemental Income Statement Elements [Abstract]
Deferred taxes on postretirement	(15)	(9)	15
Deferred taxes on unrealized gain (loss), other, tax effect	7	8	(2)
Passenger
Operating Revenue	7,665	20,776	20,455
Freight
Operating Revenue	161	172	175
Other
Operating Revenue	1,222	1,480	1,335
Fuel derivatives
Unrealized gain (loss) on derivatives, net of tax	4	(53)	(26)
Supplemental Income Statement Elements [Abstract]
Deferred taxes on unrealized gain (loss) on derivatives, tax effect	2	(16)	(7)
Interest rate derivatives
Unrealized gain (loss) on derivatives, net of tax	(25)	(25)	6
Supplemental Income Statement Elements [Abstract]
Deferred taxes on unrealized gain (loss) on derivatives, tax effect	$ (8)	$ (8)	$ 1