New Accounting Pronouncements - Adjustments (Details) $ / shares in Units, $ in Millions		3 Months Ended									12 Months Ended
		Dec. 31, 2018 USD ($) aircraft $ / shares	Sep. 30, 2018 USD ($) $ / shares	Jun. 30, 2018 USD ($) $ / shares	Mar. 31, 2018 USD ($) $ / shares	Dec. 31, 2017 USD ($) aircraft $ / shares		Sep. 30, 2017 USD ($) $ / shares	Jun. 30, 2017 USD ($) $ / shares	Mar. 31, 2017 USD ($) $ / shares	Dec. 31, 2018 USD ($) aircraft $ / shares	Dec. 31, 2017 USD ($) aircraft $ / shares	Dec. 31, 2016 USD ($) $ / shares	Jan. 01, 2019 USD ($)	Jan. 01, 2018 USD ($)
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Prepaid expenses and other current assets		$ 310				$ 460					$ 310	$ 460
Operating Revenue											21,965	21,146	$ 20,289
Accrued Liabilities, Recast		1,749				1,700					1,749	1,700
Air traffic liability		4,134				3,495					4,134	3,495
Air traffic liablity - noncurrent		936				1,070					936	1,070
Deferred income taxes		2,427				2,119					2,427	2,119
Retained earnings		$ 15,967				$ 13,832					$ 15,967	$ 13,832
Aircraft under operating lease | aircraft		51				53					51	53
Salaries, wages, and benefits											$ 7,649	$ 7,305	6,786
Fuel and oil											4,616	4,076	3,801
Other operating expenses											2,852	2,847	2,703
Other (gains) losses, net											18	112	21
PROVISION (BENEFIT) FOR INCOME TAXES											699	(92)	1,267
Net income		$ 654	$ 615	$ 733	$ 463	$ 1,747	[1]	$ 528	$ 743	$ 339	$ 2,465	$ 3,357	$ 2,183
NET INCOME PER SHARE, BASIC (in dollars per share) | $ / shares		$ 1.17	$ 1.08	$ 1.27	$ 0.79	$ 2.95	[1]	$ 0.88	$ 1.23	$ 0.55	$ 4.30	$ 5.58	$ 3.48
NET INCOME PER SHARE, DILUTED (in dollars per share) | $ / shares		$ 1.17	$ 1.08	$ 1.27	$ 0.79	$ 2.94	[1]	$ 0.88	$ 1.23	$ 0.55	$ 4.29	$ 5.57	$ 3.45
Deferred income taxes											$ 301	$ (1,066)	$ 419
Changes in certain assets and liabilities												212	279
Net Cash Provided by operating activities											4,893	3,929	4,293
Flight equipment		$ 21,753				$ 21,368					21,753	21,368
Assets constructed for others		1,768				1,543					1,768	1,543
Less allowance for depreciation and amortization		9,731				9,690					9,731	9,690
Other assets		720				786					720	786
Assets		26,243				25,110					26,243	25,110
Accounts payable		1,416				1,320					1,416	1,320
Current maturities of long-term debt		606				348					606	348
Construction obligation	[2]	1,701				1,390					1,701	1,390
Other noncurrent liabilities		650				707					650	707
Liabilities and Equity		$ 26,243				25,110					$ 26,243	25,110
Scenario, Previously Reported
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Accrued Liabilities						1,777						1,777
Air traffic liability						3,460						3,460
Air traffic liablity - noncurrent						0						0
Deferred income taxes						2,358						2,358
Retained earnings						14,621						14,621
Salaries, wages, and benefits												7,319	6,798
Fuel and oil												3,940	3,647
Other operating expenses												2,886	2,743
Other (gains) losses, net												(234)	(162)
PROVISION (BENEFIT) FOR INCOME TAXES												(237)	1,303
Net income												$ 3,488	$ 2,244
NET INCOME PER SHARE, BASIC (in dollars per share) | $ / shares												$ 5.80	$ 3.58
NET INCOME PER SHARE, DILUTED (in dollars per share) | $ / shares												$ 5.79	$ 3.55
Deferred income taxes												$ 1,212	$ (455)
Changes in certain assets and liabilities												227	182
Net Cash Provided by operating activities												3,929	4,293
Restatement Adjustment
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Assets constructed for others														$ 1,500
Accounting Standards Update 2017-07
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
New Accounting Pronouncement or Change in Accounting Principle, Effect of Adoption												14	12
Adjustments for New Accounting Standards Update 2014-09 | Restatement Adjustment
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Accrued Liabilities						(77)						(77)
Air traffic liability						35						35
Air traffic liablity - noncurrent						1,070						1,070
Deferred income taxes						(239)						(239)
Retained earnings						$ (789)						(789)
Salaries, wages, and benefits												0	0
Fuel and oil												0	0
Other operating expenses												(39)	(40)
Other (gains) losses, net												0	0
PROVISION (BENEFIT) FOR INCOME TAXES												145	(36)
Net income												$ (131)	$ (60)
NET INCOME PER SHARE, BASIC (in dollars per share) | $ / shares												$ (0.22)	$ (0.1)
NET INCOME PER SHARE, DILUTED (in dollars per share) | $ / shares												$ (0.22)	$ (0.1)
Deferred income taxes												$ (145)	$ 36
Changes in certain assets and liabilities												(14)	96
Net Cash Provided by operating activities												0	0
Adjustments for New Accounting Standards Update 2017-07 | Restatement Adjustment
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Salaries, wages, and benefits												(14)	(12)
Fuel and oil												0	0
Other operating expenses												0	0
Other (gains) losses, net												(14)	(12)
PROVISION (BENEFIT) FOR INCOME TAXES												0	0
Net income												$ 0	$ 0
NET INCOME PER SHARE, BASIC (in dollars per share) | $ / shares												$ 0	$ 0
NET INCOME PER SHARE, DILUTED (in dollars per share) | $ / shares												$ 0	$ 0
Adjustments for New Accounting Standards Update 2017-12 | Restatement Adjustment
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Salaries, wages, and benefits												$ 0	$ 0
Fuel and oil												136	154
Other operating expenses												0	0
Other (gains) losses, net												136	154
PROVISION (BENEFIT) FOR INCOME TAXES												0	0
Net income												$ 0	$ 0
NET INCOME PER SHARE, BASIC (in dollars per share) | $ / shares												$ 0	$ 0
NET INCOME PER SHARE, DILUTED (in dollars per share) | $ / shares												$ 0	$ 0
Accumulated other comprehensive income (loss) | Adjustments for New Accounting Standards Update 2014-09 | Restatement Adjustment
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Retained earnings															$ 20
B-717-200
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Aircraft under operating lease | aircraft		73									73
Passenger
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Operating Revenue											$ 20,455	$ 19,763	$ 19,068
Passenger | Scenario, Previously Reported
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Operating Revenue												19,141	18,594
Passenger | Adjustments for New Accounting Standards Update 2014-09 | Restatement Adjustment
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Operating Revenue												622	474
Passenger | Adjustments for New Accounting Standards Update 2017-07 | Restatement Adjustment
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Operating Revenue												0	0
Passenger | Adjustments for New Accounting Standards Update 2017-12 | Restatement Adjustment
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Operating Revenue												0	0
Other
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Operating Revenue											$ 1,335	1,210	1,050
Other | Scenario, Previously Reported
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Operating Revenue												1,857	1,660
Other | Adjustments for New Accounting Standards Update 2014-09 | Restatement Adjustment
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Operating Revenue												(647)	(610)
Other | Adjustments for New Accounting Standards Update 2017-07 | Restatement Adjustment
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Operating Revenue												0	0
Other | Adjustments for New Accounting Standards Update 2017-12 | Restatement Adjustment
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Operating Revenue												$ 0	$ 0

[1] Includes a $1.3 billion reduction in Provision for income taxes related to the Tax Cuts and Jobs Act legislation enacted in December 2017, which resulted in a re-measurement of the Company's deferred tax assets and liabilities at the new federal corporate tax rate of 21 percent. See Note 14 to the Consolidated Financial Statements for further information.

[2] Construction obligation will be reduced through future facility rent payments. These future payments are not fixed per the lease agreement, but are variable and fluctuate based on various market and other factors outside the control of the Company.