COVID-19 PANDEMIC (Details) $ in Millions	3 Months Ended			6 Months Ended
	Jun. 30, 2020 USD ($) aircraft	Mar. 31, 2020 USD ($)	Jun. 30, 2019 USD ($)	Jun. 30, 2020 USD ($) aircraft	Jun. 30, 2019 USD ($)	Aug. 31, 2020 USD ($)	Jun. 23, 2020 USD ($)	Apr. 23, 2020 USD ($)	Dec. 31, 2019 USD ($)
Impaired Long-Lived Assets [Line Items]
Asset Impairment Charges				$ 214.0
Number of Mainline Aircraft Parked | aircraft	101			101
ProceedsFromPayrollSupportProgramGrant				$ 723.0	$ 0.0
Unsecured Term Loan through PSP of CARES Act	$ 276.0			276.0					$ 0.0
Impairment of Intangible Assets, Finite-lived				10.0
Accounts Receivable, Allowance for Credit Loss, Writeoff				$ 5.0
Number of Mainline Aircraft Parked | aircraft	101			101
ProceedsFromPayrollSupportProgramGrant				$ 723.0	0.0
PSPGrantRecognized	$ (362.0)		$ 0.0	(362.0)	$ 0.0
Unsecured Term Loan through PSP of CARES Act	276.0			276.0					$ 0.0
Alaska Airlines and Horizon Air [Member]
Impaired Long-Lived Assets [Line Items]
Total Expected Relief From PSP of CARES Act								$ 992.0
Total Expected Relief From PSP of CARES Act								$ 992.0
McGee Air Services [Member]
Impaired Long-Lived Assets [Line Items]
Total Expected Relief From PSP of CARES Act							$ 30.0
PSP Installments Received							15.0
Total Expected Relief From PSP of CARES Act							30.0
PSP Installments Received							$ 15.0
Subsequent Event [Member] | McGee Air Services [Member]
Impaired Long-Lived Assets [Line Items]
PSP Installments Received						$ 15.0
Unsecured Term Loan through PSP of CARES Act						5.0
Unsecured Term Loan through PSP of CARES Act						5.0
PSP Installments Received						$ 15.0
Aircraft [Member]
Impaired Long-Lived Assets [Line Items]
Asset Impairment Charges				69.0
Operating Lease Asset
Impaired Long-Lived Assets [Line Items]
Asset Impairment Charges				62.0
Disposal Group, Held-for-sale, Not Discontinued Operations
Impaired Long-Lived Assets [Line Items]
Asset Impairment Charges				3.0
Inventories
Impaired Long-Lived Assets [Line Items]
Asset Impairment Charges				2.0
Lease Return Costs
Impaired Long-Lived Assets [Line Items]
Asset Impairment Charges				78.0
Airbus [Member]
Impaired Long-Lived Assets [Line Items]
Asset Impairment Charges	$ 70.0	$ 83.0		153.0
Aircraft Permanently Parked | aircraft	12
Aircraft Permanently Parked | aircraft	12
Airbus [Member] | Aircraft [Member]
Impaired Long-Lived Assets [Line Items]
Asset Impairment Charges				11.0
Airbus [Member] | Operating Lease Asset
Impaired Long-Lived Assets [Line Items]
Asset Impairment Charges				62.0
Airbus [Member] | Disposal Group, Held-for-sale, Not Discontinued Operations
Impaired Long-Lived Assets [Line Items]
Asset Impairment Charges				0.0
Airbus [Member] | Inventories
Impaired Long-Lived Assets [Line Items]
Asset Impairment Charges				2.0
Airbus [Member] | Lease Return Costs
Impaired Long-Lived Assets [Line Items]
Asset Impairment Charges				78.0
Q400 [Member]
Impaired Long-Lived Assets [Line Items]
Asset Impairment Charges				61.0
Aircraft Permanently Parked | aircraft	2
Aircraft Permanently Parked | aircraft	2
Q400 [Member] | Aircraft [Member]
Impaired Long-Lived Assets [Line Items]
Asset Impairment Charges				58.0
Q400 [Member] | Operating Lease Asset
Impaired Long-Lived Assets [Line Items]
Asset Impairment Charges				0.0
Q400 [Member] | Disposal Group, Held-for-sale, Not Discontinued Operations
Impaired Long-Lived Assets [Line Items]
Asset Impairment Charges				3.0
Q400 [Member] | Inventories
Impaired Long-Lived Assets [Line Items]
Asset Impairment Charges				0.0
Q400 [Member] | Lease Return Costs
Impaired Long-Lived Assets [Line Items]
Asset Impairment Charges				$ 0.0