Summary of Significant Accounting Policies (Details)	12 Months Ended
	Dec. 31, 2020 USD ($) aircraft	Dec. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)
Accounting Policies [Abstract]
Capitalized computer software, net	$ 697,000,000	$ 630,000,000
Computer software depreciation expense	203,000,000	177,000,000	$ 155,000,000
Capitalized computer software, Impairments	0
Advertising costs	156,000,000	212,000,000	215,000,000
Loss on asset impairment	$ (32,000,000)	0	0
Concentration Risk [Line Items]
Percentage Of Employees Represented By Unions Under Collective Bargaining Agreements in Negotiations	55.00%
Number of Aircraft Grounded Under Emergency Order on March 13, 2019 | aircraft	34
Indefinite-Lived Intangible Assets [Line Items]
Goodwill impairment	$ 0
Length of agreements with co-brand, payment, and loyalty partners	10 years
Operating Revenue	$ 9,048,000,000	22,428,000,000	21,965,000,000
Fuel derivatives
Change in Accounting Estimate [Line Items]
Collateral Already Posted, Aggregate Fair Value	34,000,000
Total collateral already posted aggregate fair value	34,000,000	25,000,000
Other Intangible Assets
Indefinite-Lived Intangible Assets [Line Items]
Gross carrying amount of indefinite-lived intangible assets	295,000,000	295,000,000
Other Noncurrent Liabilities | Interest rate derivatives
Change in Accounting Estimate [Line Items]
Collateral Already Posted, Aggregate Fair Value	$ 0	0
Flight equipment
Property, Plant and Equipment [Line Items]
Maximum percentage of cost estimated as residual value (in hundredths)	15.00%
Flight equipment | Maximum
Property, Plant and Equipment [Line Items]
Property, Plant, and Equipment Useful Life	25 years
Ground property and equipment
Property, Plant and Equipment [Line Items]
Minimum percentage of cost estimated residual value (in hundredths)	0.00%
Maximum percentage of cost estimated as residual value (in hundredths)	10.00%
Ground property and equipment | Minimum
Property, Plant and Equipment [Line Items]
Property, Plant, and Equipment Useful Life	5 years
Ground property and equipment | Maximum
Property, Plant and Equipment [Line Items]
Property, Plant, and Equipment Useful Life	30 years
Software | Minimum
Property, Plant and Equipment [Line Items]
Property, Plant, and Equipment Useful Life	5 years
Software | Maximum
Property, Plant and Equipment [Line Items]
Property, Plant, and Equipment Useful Life	15 years
Latin America
Operating Revenue	$ 184,000,000	615,000,000	566,000,000
North America
Operating Revenue	$ 8,900,000,000	$ 21,800,000,000	$ 21,400,000,000
Unionized Employees concentration risk
Concentration Risk [Line Items]
The percentage of Company's employees that are unionized and covered by collective bargaining agreements (in hundredths)	83.00%
B-737-700
Property, Plant and Equipment [Line Items]
Total aircraft retired in 4Q20 | aircraft	20