Quarterly Financial Data (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended									12 Months Ended
	Dec. 31, 2020	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019		Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Quarterly Financial Data [Abstract]
Operating revenues	$ 2,013	$ 1,793	$ 1,008	$ 4,234	$ 5,729		$ 5,639	$ 5,909	$ 5,149
Operating income (loss)	(1,169)	(1,411)	(1,127)	(110)	665		819	968	505	$ (3,816)	$ 2,957	$ 3,206
INCOME (LOSS) BEFORE INCOME TAXES	(1,331)	(1,542)	(1,239)	(144)	666		819	968	504	(4,256)	2,957	3,164
Net income (loss)	$ (908)	$ (1,157)	$ (915)	$ (94)	$ 514	[1]	$ 659	$ 741	$ 387	$ (3,074)	$ 2,300	$ 2,465
NET INCOME (LOSS) PER SHARE, BASIC	$ (1.54)	$ (1.96)	$ (1.63)	$ (0.18)	$ 0.98	[1]	$ 1.24	$ 1.37	$ 0.70	$ (5.44)	$ 4.28	$ 4.30
NET INCOME (LOSS) PER SHARE, DILUTED	$ (1.54)	$ (1.96)	$ (1.63)	$ (0.18)	$ 0.98	[1]	$ 1.23	$ 1.37	$ 0.70	$ (5.44)	$ 4.27	$ 4.29
Discretionary Profitsharing Related to Impact of Aircraft Grounded Under Emergency Order					$ 124
Net Income Impact of 2019 Discretionary Profitsharing					$ 97
Net Income per Share Impact of 2019 Discretionary Profitsharing					$ 0.18

[1] In addition to the ongoing impact of the Boeing 737 MAX aircraft ("MAX") grounding that impacted all four quarters of 2019, fourth quarter 2019 also included the impact of the pre-tax $124 million discretionary, special profitsharing award accrual authorized by the Company's Board of Directors during fourth quarter 2019 for compensation received from Boeing related to the Company's estimated 2019 financial damages related to the grounding of the Boeing 737 MAX. See Note 17 to the Consolidated Financial Statements for further information on the MAX groundings. The impact of this accrual resulted in a decrease to Net income of approximately $97 million and reduced Basic and Diluted net income per share by approximately $.18 for the fourth quarter 2019.