FLEET TRANSITION (Details) $ in Millions	3 Months Ended			6 Months Ended
	Mar. 31, 2024 airline	Jun. 30, 2023 USD ($) airline	Jun. 30, 2022 USD ($)	Dec. 31, 2023 airline	Jun. 30, 2023 USD ($)	Jun. 30, 2022 USD ($)	Jul. 31, 2023 USD ($)
Impaired Long-Lived Assets [Line Items]
Special items - Impairment charges and other		$ 186	$ 146		$ 199	$ 221
Finance Lease, Right-of-Use Asset, after Accumulated Amortization		175			175
Finance Lease, Liability		316			316
Accelerated aircraft ownership expenses [Member]
Impaired Long-Lived Assets [Line Items]
Special items - Impairment charges and other		19	43		25	43
Lease return costs and other expenses
Impaired Long-Lived Assets [Line Items]
Special items - Impairment charges and other		16	103		23	108
Fleet transition - impairment [Member]
Impaired Long-Lived Assets [Line Items]
Special items - Impairment charges and other		$ 151	$ 0		$ 151	$ 70
A321neo [Member]
Impaired Long-Lived Assets [Line Items]
Number of Aircraft Operated | airline		10
Finance Lease, Impairment Loss		$ 156
A321neo [Member] | Aircraft purchase [Member]
Impaired Long-Lived Assets [Line Items]
Number of Aircraft Operated | airline		1
A321neo [Member] | New firm aircraft commitment [Member]
Impaired Long-Lived Assets [Line Items]
Number of Aircraft Operated | airline		6
A321neo [Member] | Subsequent Event [Member]
Impaired Long-Lived Assets [Line Items]
2024							$ 130
A321neo [Member] | Subsequent Event [Member] | Aircraft purchase [Member]
Impaired Long-Lived Assets [Line Items]
Number of Aircraft Operated | airline	2			5