Recently Issued Accounting Standards - Schedule of Adoption of ASC 606 and Expected Impact (Statement of Operations) (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended			9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017		Sep. 30, 2018	Sep. 30, 2017
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Revenue	$ 11,003	$ 9,899	[1]	$ 30,812	$ 28,333	[2]
Salaries and related costs	2,930	2,785	[2]	8,534	8,263	[2]
Distribution expenses	427	377	[2]	1,162	1,081	[2]
Other operating expenses	1,467	1,436	[2]	4,293	4,126	[2]
Total operating expenses	9,800	8,761	[2]	28,172	25,438	[2]
Operating income	1,203	1,138	[2]	2,640	2,895	[2]
Interest expense	(187)	(169)	[2]	(540)	(498)	[2]
Miscellaneous, net	(1)	(13)	[2]	(119)	(82)	[2]
Total nonoperating expense, net	(142)	(145)	[2]	(538)	(475)	[2]
Income before income taxes	1,061	993	[2]	2,102	2,420	[2]
Income tax expense	225	348	[2]	435	855	[2]
Net income	$ 836	$ 645	[2],[3]	$ 1,667	$ 1,565	[2],[3]
Earnings per share, basic (in dollars per share)	$ 3.07	$ 2.15	[2]	$ 6.02	$ 5.10	[2]
Earnings per share, diluted (in dollars per share)	$ 3.06	$ 2.15	[2]	$ 5.99	$ 5.09	[2]
As Previously Reported
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Revenue		$ 9,878			$ 28,298
Salaries and related costs		2,812			8,341
Distribution expenses		352			1,021
Other operating expenses		1,459			4,199
Total operating expenses		8,786			25,529
Operating income		1,092			2,769
Interest expense		(164)			(472)
Miscellaneous, net		15			(3)
Total nonoperating expense, net		(112)			(370)
Income before income taxes		980			2,399
Income tax expense		343			848
Net income		$ 637			$ 1,551
Earnings per share, basic (in dollars per share)		$ 2.12			$ 5.06
Earnings per share, diluted (in dollars per share)		$ 2.12			$ 5.04
Restatement Adjustment | Accounting Standards Update 2014-09
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Revenue		$ 21			$ 35
Salaries and related costs		0			0
Distribution expenses		25			60
Other operating expenses		(23)			(73)
Total operating expenses		2			(13)
Operating income		19			48
Interest expense		(5)			(26)
Miscellaneous, net		(1)			(1)
Total nonoperating expense, net		(6)			(27)
Income before income taxes		13			21
Income tax expense		5			7
Net income		$ 8			$ 14
Earnings per share, basic (in dollars per share)		$ 0.03			$ 0.04
Earnings per share, diluted (in dollars per share)		$ 0.03			$ 0.05
Restatement Adjustment | Accounting Standards Update 2017-07
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Salaries and related costs		$ (27)			$ (78)
Distribution expenses		0			0
Other operating expenses		0			0
Total operating expenses		(27)			(78)
Operating income		27			78
Interest expense		0			0
Miscellaneous, net		(27)			(78)
Total nonoperating expense, net		(27)			(78)
Income before income taxes		0			0
Income tax expense		0			0
Net income		$ 0			$ 0
Earnings per share, basic (in dollars per share)		$ 0.00			$ 0.00
Earnings per share, diluted (in dollars per share)		$ 0.00			$ 0.00
Passenger revenue
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Revenue	$ 10,120	$ 9,069	[1]	$ 28,150	$ 25,873	[2]
Passenger revenue | As Previously Reported
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Revenue		8,528			24,324
Passenger revenue | Restatement Adjustment | Accounting Standards Update 2014-09
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Revenue		541			1,549
Cargo
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Revenue	296	279	[1]	903	790	[2]
Cargo | As Previously Reported
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Revenue		257			731
Cargo | Restatement Adjustment | Accounting Standards Update 2014-09
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Revenue		22			59
Other operating revenue
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Revenue	$ 587	551	[1]	$ 1,759	1,670	[2]
Other operating revenue | As Previously Reported
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Revenue		1,093			3,243
Other operating revenue | Restatement Adjustment | Accounting Standards Update 2014-09
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Revenue		$ (542)			$ (1,573)

[1] Amounts adjusted due to the adoption of Accounting Standards Update No. 2014-09, Revenue from Contracts with Customers (Topic 606) and Accounting Standards Update No. 2017-07, Improving the Presentation of Net Periodic Pension Cost and Net Periodic Postretirement Benefit Cost. See Note 1 to the financial statements contained in Part I, Item 1 of this report for additional information.

[2] Amounts adjusted due to the adoption of Accounting Standards Update No. 2014-09, Revenue from Contracts with Customers (Topic 606) and Accounting Standards Update No. 2017-07, Improving the Presentation of Net Periodic Pension Cost and Net Periodic Postretirement Benefit Cost. See Note 1 to the financial statements contained in Part I, Item 1 of this report for additional information.

[3] Amounts adjusted due to the adoption of Accounting Standards Update No. 2014-09, Revenue from Contracts with Customers (Topic 606) and Accounting Standards Update No. 2017-07, Improving the Presentation of Net Periodic Pension Cost and Net Periodic Postretirement Benefit Cost. See Note 1 to the financial statements contained in Part I, Item 1 of this report for additional information.