Net Income (Loss) Per Share (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	3 Months Ended									12 Months Ended
	Dec. 31, 2020	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	[1]	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
NUMERATOR:
Net income (loss)	$ (908)	$ (1,157)	$ (915)	$ (94)	$ 514		$ 659	$ 741	$ 387	$ (3,074)	$ 2,300	$ 2,465
DENOMINATOR:
Weighted-average shares outstanding, basic										565	538	573
Dilutive effect of restricted stock units										0	1	1
Adjusted weighted-average shares outstanding, diluted										565	539	574
NET INCOME (LOSS) PER SHARE:
NET INCOME (LOSS) PER SHARE, BASIC	$ (1.54)	$ (1.96)	$ (1.63)	$ (0.18)	$ 0.98		$ 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		$ 1.23	$ 1.37	$ 0.70	$ (5.44)	$ 4.27	$ 4.29

[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.