COMMITMENTS AND CONTINGENCIES COMMITMENTS AND CONTINGENCIES (Details)	12 Months Ended		20 Months Ended
	Dec. 31, 2020 USD ($) aircraft	Dec. 31, 2018 USD ($)	Dec. 31, 2020 USD ($) aircraft
Unrecorded Unconditional Purchase Obligation, Fiscal Year Maturity [Abstract]
Rent expense		$ 619,000,000
Payments for Construction in Process			$ 24,000,000
LAX Construction, Amount Reimbursed			8,700,000
LAX Redevelopment Project, Total Expected Outlay	$ 230,000,000		230,000,000
Virgin America Flight Attendants [Member]
Unrecorded Unconditional Purchase Obligation, Fiscal Year Maturity [Abstract]
Loss Contingency, Damages Sought, Value	78,000,000
Loss Contingency, Damages Sought, Value	78,000,000
Aircraft Commitments [Member]
Unrecorded Unconditional Purchase Obligation, Fiscal Year Maturity [Abstract]
2021	873,000,000		873,000,000
2022	372,000,000		372,000,000
2023	238,000,000		238,000,000
2024	27,000,000		27,000,000
2025	16,000,000		16,000,000
Thereafter	13,000,000		13,000,000
Total	1,539,000,000		1,539,000,000
Capacity Purchase Agreements[Member]
Unrecorded Unconditional Purchase Obligation, Fiscal Year Maturity [Abstract]
2021	166,000,000		166,000,000
2022	174,000,000		174,000,000
2023	179,000,000		179,000,000
2024	184,000,000		184,000,000
2025	189,000,000		189,000,000
Thereafter	690,000,000		690,000,000
Total	$ 1,582,000,000		$ 1,582,000,000
B737
Unrecorded Unconditional Purchase Obligation, Fiscal Year Maturity [Abstract]
Commited to purchase (in aircraft) | aircraft	32		32
Option to purchase additional (in aircraft) | aircraft	37		37
A-320-Neo [Member]
Unrecorded Unconditional Purchase Obligation, Fiscal Year Maturity [Abstract]
Option to purchase additional (in aircraft) | aircraft	30		30
B737 MAX [Member]
Unrecorded Unconditional Purchase Obligation, Fiscal Year Maturity [Abstract]
Commited to purchase (in aircraft) | aircraft	23		23
Option to purchase additional (in aircraft) | aircraft	15		15
E175 [Member]
Unrecorded Unconditional Purchase Obligation, Fiscal Year Maturity [Abstract]
Commited to purchase (in aircraft) | aircraft	3		3
Option to purchase additional (in aircraft) | aircraft	30		30
Capacity Purchase Agreement with SkyWest [Member] | E175 [Member]
Unrecorded Unconditional Purchase Obligation, Fiscal Year Maturity [Abstract]
Property Subject to or Available for Operating Lease, Number of Optional Additional Units | aircraft	8		8
Property Subject to Operating Lease [Member] | B737
Unrecorded Unconditional Purchase Obligation, Fiscal Year Maturity [Abstract]
Operating leases, number of leased assets (in aircraft) | aircraft	10		10
Property Subject to Operating Lease [Member] | Q400
Unrecorded Unconditional Purchase Obligation, Fiscal Year Maturity [Abstract]
Operating leases, number of leased assets (in aircraft) | aircraft	7		7
Property Subject to Operating Lease [Member] | Airbus
Unrecorded Unconditional Purchase Obligation, Fiscal Year Maturity [Abstract]
Operating leases, number of leased assets (in aircraft) | aircraft	71		71
Property Subject to Operating Lease [Member] | E175 [Member]
Unrecorded Unconditional Purchase Obligation, Fiscal Year Maturity [Abstract]
Operating leases, number of leased assets (in aircraft) | aircraft	32		32