Summary of Significant Accounting Policies - Long-Lived Assets (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Property, Plant and Equipment [Line Items]
Less: accumulated depreciation and amortization	$ (17,027)	$ (15,823)
Total property and equipment, net	31,310	28,335
Flight equipment
Property, Plant and Equipment [Line Items]
Property and equipment, gross	$ 36,713	33,898
Flight equipment | Minimum
Property, Plant and Equipment [Line Items]
Estimated useful life	20 years
Flight equipment | Maximum
Property, Plant and Equipment [Line Items]
Estimated useful life	34 years
Ground property and equipment
Property, Plant and Equipment [Line Items]
Property and equipment, gross	$ 5,721	4,667
Ground property and equipment | Minimum
Property, Plant and Equipment [Line Items]
Estimated useful life	3 years
Ground property and equipment | Maximum
Property, Plant and Equipment [Line Items]
Estimated useful life	40 years
Information technology-related assets
Property, Plant and Equipment [Line Items]
Property and equipment, gross	$ 3,276	3,361
Information technology-related assets | Minimum
Property, Plant and Equipment [Line Items]
Estimated useful life	3 years
Information technology-related assets | Maximum
Property, Plant and Equipment [Line Items]
Estimated useful life	15 years
Flight and ground equipment under capital lease
Property, Plant and Equipment [Line Items]
Property and equipment, gross	$ 1,608	1,055
Less: accumulated depreciation and amortization	(546)	(566)
Advance payments for equipment
Property, Plant and Equipment [Line Items]
Property and equipment, gross	$ 1,019	$ 1,177