COVID-19 PANDEMIC NARRATIVE (Details)	12 Months Ended			60 Months Ended
	Dec. 31, 2020 USD ($) aircraft shares	Dec. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)	Apr. 22, 2030	Feb. 05, 2021 USD ($)	Jan. 15, 2021 USD ($) shares	Dec. 24, 2020 $ / shares	Apr. 23, 2020 $ / shares
Concentration Risk [Line Items]
Number of Mainline Aircraft Parked | aircraft	32
Asset Impairment Charges	$ 363,000,000
Leased Aircraft Return Costs	209,000,000
Impairment of Intangible Assets, Finite-lived	10
Restructuring Charges	220,000,000	$ 0	$ 0
Restructuring Reserve	127,000,000
Aircraft Purchase Deposit, Write-off	15,000,000
Accounts Receivable, Allowance for Credit Loss, Writeoff	5,000,000
Special Items - Impairment charges and other	627,000,000	0	$ 0
Total Expected Relief from PSP of CARES Act	1,100,000,000
Unsecured Term Loan through PSP of CARES Act	290,000,000	$ 0
Line of credit facility, borrowing capacity	461,000,000
Proceeds from Lines of Credit	400,000,000
CARES Act Payroll Tax Relief	29,000,000
Adjustments to Additional Paid in Capital, Warrant Issued	14,000,000
Proceeds From Payroll Support Program Grant	$ 753,000,000
Airbus
Concentration Risk [Line Items]
Aircraft Permanently Parked | aircraft	40
Asset Impairment Charges	$ 302,000,000
Q400
Concentration Risk [Line Items]
Asset Impairment Charges	61,000,000
ALK Common Stock Warrant
Concentration Risk [Line Items]
Class of Warrant or Right, Exercise Price of Warrants or Rights | $ / shares							$ 52.25	$ 31.61
Subsequent Event
Concentration Risk [Line Items]
Unsecured Term Loan through PSP of CARES Act					$ 130,000,000	$ 51,000,000
Total Relief from Extension of PSP						$ 546,000,000
Subsequent Event | ALK Common Stock Warrant
Concentration Risk [Line Items]
Class of Warrant or Right, Number of Securities Called by Warrants or Rights | shares						101,227
Subsequent Event | Alaska Airlines and Horizon Air
Concentration Risk [Line Items]
PSP Installments Received						$ 266,000,000
Subsequent Event | McGee Air Services
Concentration Risk [Line Items]
PSP Installments Received					$ 6,000,000
CARES Act PSP Term Loan
Concentration Risk [Line Items]
Adjustments to Additional Paid in Capital, Warrant Issued	8,000,000
US Treasury CARES Act Loan
Concentration Risk [Line Items]
Line of credit facility, borrowing capacity	1,900,000,000
Proceeds from Lines of Credit	$ 135,000,000
Class of Warrant or Right, Number of Securities Called by Warrants or Rights | shares	427,080
Adjustments to Additional Paid in Capital, Warrant Issued	$ 6,000,000
CARES Act Unsecured Interest Rate
Concentration Risk [Line Items]
Debt Instrument, Interest Rate, Stated Percentage	1.00%
CARES Act Unsecured Interest Rate | Subsequent Event
Concentration Risk [Line Items]
Debt Instrument, Basis Spread on Variable Rate				2.00%