Special Charges and Mark-to-Market ("MTM") Adjustments - Narrative (Details) Employee in Thousands	1 Months Ended	3 Months Ended			9 Months Ended
	May 31, 2018 USD ($)	Sep. 30, 2019 USD ($)	Sep. 30, 2018 USD ($)	Mar. 31, 2017 USD ($) Employee	Sep. 30, 2019 USD ($)	Sep. 30, 2018 USD ($)
Restructuring Cost and Reserve [Line Items]
Early lease termination charge		$ 6,000,000
Other miscellaneous impairments		8,000,000
Fair value adjustment for aircraft purchased off lease and impairments related to certain fleet types and certain international slots no longer in use			$ 11,000,000		$ 8,000,000	$ 40,000,000
Severance and benefit costs		2,000,000	9,000,000		14,000,000	34,000,000
(Gains) losses on sale of assets and other special charges		(25,000,000)	3,000,000		(33,000,000)	(7,000,000)
Charge for the settlement of certain legal matters		18,000,000
Charge related to a contract termination		15,000,000
Gain (loss) on the sale and disposition of assets		8,000,000			(8,000,000)
Loss recorded for the change in fair value of certain derivative assets		4,000,000			5,000,000
Use Rights
Restructuring Cost and Reserve [Line Items]
Write off of intangible asset	$ 105,000,000
Azul
Restructuring Cost and Reserve [Line Items]
Gain (loss) for the change in fair value of equity investments		25,000,000	29,000,000		77,000,000	(61,000,000)
Management
Restructuring Cost and Reserve [Line Items]
Severance and benefit costs		2,000,000	4,000,000		12,000,000	15,000,000
International Brotherhood of Teamsters | Voluntary Early-Out Program
Restructuring Cost and Reserve [Line Items]
Severance and benefit costs			$ 5,000,000		$ 2,000,000	$ 19,000,000
Number of technicians and related employees electing to voluntarily separate from the Company | Employee				1
Severance payment per participant (up to)				$ 100,000
Aircraft Engines
Restructuring Cost and Reserve [Line Items]
Impairment of assets removed from operations		$ 47,000,000