Quarterly Financial Data (Details) - USD ($) $ / shares in Units, $ in Millions		3 Months Ended									12 Months Ended
		Dec. 31, 2019		Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Quarterly Financial Data [Abstract]
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
Operating revenues		$ 5,729		$ 5,639	$ 5,909	$ 5,149	$ 5,704	$ 5,575	$ 5,742	$ 4,944
Operating income		665		819	968	505	820	798	972	616	$ 2,957	$ 3,206	$ 3,407
Income before income taxes		666		819	968	504	817	786	960	602	2,957	3,164	3,265
Net income		$ 514	[1]	$ 659	$ 741	$ 387	$ 654	$ 615	$ 733	$ 463	$ 2,300	$ 2,465	$ 3,357
Basic (in dollars per share)		$ 0.98	[1]	$ 1.24	$ 1.37	$ 0.70	$ 1.17	$ 1.08	$ 1.27	$ 0.79	$ 4.28	$ 4.30	$ 5.58
Diluted (in dollars per share)		$ 0.98	[1]	$ 1.23	$ 1.37	$ 0.70	$ 1.17	$ 1.08	$ 1.27	$ 0.79	$ 4.27	$ 4.29	$ 5.57
Change in federal statutory rate	[2]										$ 31	$ 0	$ 1,270

[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 16 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.

[2] The Tax Cuts and Jobs Act was enacted in December 2017, which reduced the U.S. federal corporate tax rate from the previous rate of 35 percent to 21 percent