The aggregate expense charged against earnings to allocate the cost of intangible assets (nonphysical assets not used in production) in a systematic and rational manner to the periods expected to benefit from such assets. As a noncash expense, this element is added back to net income when calculating cash provided by or used in operations using the indirect method.

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Stated as a percentage, the estimated or actual value of the asset at the end of its useful life or when it is no longer serviceable (cannot be used for its original purpose) divided by its [historical] capitalized cost.

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Useful life of long lived, physical assets used in the normal conduct of business and not intended for resale, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days. Examples include, but not limited to, land, buildings, machinery and equipment, office equipment, furniture and fixtures, and computer equipment.

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Summary of Significant Accounting Policies - Property, Plant and Equipment (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Property, Plant and Equipment [Line Items]
Depreciation	$ 50	$ 44	$ 38
Intangible amortization	0	1	0
Total depreciation and amortization	50	45	$ 38
Property and equipment, net	$ 309	226
Aircraft and spare engines
Property, Plant and Equipment [Line Items]
Useful life	25 years
Residual Value	10.00%
Flight equipment
Property, Plant and Equipment [Line Items]
Residual Value	0.00%
Aircraft rotable parts
Property, Plant and Equipment [Line Items]
Residual Value	10.00%
Ground property and equipment
Property, Plant and Equipment [Line Items]
Residual Value	0.00%
Ground property and equipment \| Minimum
Property, Plant and Equipment [Line Items]
Useful life	3 years
Ground property and equipment \| Maximum
Property, Plant and Equipment [Line Items]
Useful life	10 years
Ground equipment leasehold improvements
Property, Plant and Equipment [Line Items]
Residual Value	0.00%
Ground equipment leasehold improvements \| Maximum
Property, Plant and Equipment [Line Items]
Useful life	10 years
Internal-use software
Property, Plant and Equipment [Line Items]
Residual Value	0.00%
Property and equipment, net	$ 13	10
Internal-use software \| Minimum
Property, Plant and Equipment [Line Items]
Useful life	3 years
Internal-use software \| Maximum
Property, Plant and Equipment [Line Items]
Useful life	10 years
Capitalized maintenance
Property, Plant and Equipment [Line Items]
Residual Value	0.00%
Property and equipment, net	$ 99	$ 46
Buildings
Property, Plant and Equipment [Line Items]
Residual Value	10.00%
Buildings \| Maximum
Property, Plant and Equipment [Line Items]
Useful life	40 years