COVID-19 PANDEMIC (Details)	3 Months Ended					9 Months Ended
	Dec. 31, 2020 USD ($)	Sep. 30, 2020 USD ($) aircraft	Jun. 30, 2020 USD ($)	Mar. 31, 2020 USD ($) aircraft	Sep. 30, 2019 USD ($)	Sep. 30, 2020 USD ($) aircraft	Sep. 30, 2019 USD ($)	Oct. 30, 2020 USD ($)	Sep. 26, 2020 USD ($)	Jun. 23, 2020 USD ($)	Apr. 23, 2020 USD ($)	Dec. 31, 2019 USD ($)
Impaired Long-Lived Assets [Line Items]
Asset Impairment Charges						$ 335,000,000
Number of Mainline Aircraft Parked | aircraft		64				64
ProceedsFromPayrollSupportProgramGrant						$ 753,000,000	$ 0
Total Expected Relief From PSP of CARES Act		$ 1,100,000,000				1,100,000,000
Unsecured Term Loan through PSP of CARES Act		290,000,000				290,000,000						$ 0
Assets Held-for-sale, Long Lived, Fair Value Disclosure		219,000,000				219,000,000
Line of Credit Facility, Maximum Borrowing Capacity		461,000,000				461,000,000
PSPGrantRecognized		(398,000,000)			$ 0	(760,000,000)	0
Adjustments to Additional Paid in Capital, Warrant Issued		$ 9,000,000	$ 7,000,000
Impairment of Intangible Assets, Finite-lived						10,000,000
Accounts Receivable, Allowance for Credit Loss, Writeoff						$ 5,000,000
Number of Mainline Aircraft Parked | aircraft		64				64
ProceedsFromPayrollSupportProgramGrant						$ 753,000,000	0
PSPGrantRecognized		$ (398,000,000)			$ 0	(760,000,000)	$ 0
Total Expected Relief From PSP of CARES Act		1,100,000,000				1,100,000,000
Unsecured Term Loan through PSP of CARES Act		290,000,000				290,000,000						$ 0
Line of Credit Facility, Maximum Borrowing Capacity		461,000,000				461,000,000
Proceeds from Lines of Credit						400,000,000
CARES Act Payroll Tax Relief						17,000,000
Adjustments to Additional Paid in Capital, Warrant Issued		9,000,000	7,000,000
US Treasury CARES Act Loan [Member]
Impaired Long-Lived Assets [Line Items]
Line of Credit Facility, Maximum Borrowing Capacity		1,300,000,000				1,300,000,000
Adjustments to Additional Paid in Capital, Warrant Issued						6,000,000
Line of Credit Facility, Maximum Borrowing Capacity		$ 1,300,000,000				1,300,000,000
Proceeds from Lines of Credit						135,000,000
Adjustments to Additional Paid in Capital, Warrant Issued						6,000,000
CARES Act PSP Term Loan [Member]
Impaired Long-Lived Assets [Line Items]
Adjustments to Additional Paid in Capital, Warrant Issued						8,000,000
Adjustments to Additional Paid in Capital, Warrant Issued						8,000,000
Alaska Airlines and Horizon Air [Member]
Impaired Long-Lived Assets [Line Items]
Total Expected Relief From PSP of CARES Act											$ 992,000,000
Additional Relief from PSP of CARES Act									$ 29,000,000
Total Expected Relief From PSP of CARES Act											$ 992,000,000
Additional Relief from PSP of CARES Act									$ 29,000,000
McGee Air Services [Member]
Impaired Long-Lived Assets [Line Items]
Total Expected Relief From PSP of CARES Act										$ 30,000,000
Total Expected Relief From PSP of CARES Act										$ 30,000,000
Subsequent Event [Member]
Impaired Long-Lived Assets [Line Items]
PSPGrantRecognized	$ 10,000,000
PSPGrantRecognized	$ 10,000,000
Subsequent Event [Member] | US Treasury CARES Act Loan [Member]
Impaired Long-Lived Assets [Line Items]
Line of Credit Facility, Maximum Borrowing Capacity								$ 1,900,000,000
Line of Credit Facility, Maximum Borrowing Capacity								$ 1,900,000,000
Aircraft [Member]
Impaired Long-Lived Assets [Line Items]
Asset Impairment Charges						190,000,000
Operating Lease Asset
Impaired Long-Lived Assets [Line Items]
Asset Impairment Charges						62,000,000
Disposal Group, Held-for-sale, Not Discontinued Operations
Impaired Long-Lived Assets [Line Items]
Asset Impairment Charges						3,000,000
Inventories
Impaired Long-Lived Assets [Line Items]
Asset Impairment Charges						2,000,000
Lease Return Costs
Impaired Long-Lived Assets [Line Items]
Asset Impairment Charges						78,000,000
Airbus [Member]
Impaired Long-Lived Assets [Line Items]
Asset Impairment Charges			$ 70,000,000	$ 83,000,000		274,000,000
Aircraft Permanently Parked | aircraft		8		12
Aircraft Permanently Parked | aircraft		8		12
Airbus [Member] | Aircraft [Member]
Impaired Long-Lived Assets [Line Items]
Asset Impairment Charges						132,000,000
Airbus [Member] | Operating Lease Asset
Impaired Long-Lived Assets [Line Items]
Asset Impairment Charges						62,000,000
Airbus [Member] | Disposal Group, Held-for-sale, Not Discontinued Operations
Impaired Long-Lived Assets [Line Items]
Asset Impairment Charges						0
Airbus [Member] | Inventories
Impaired Long-Lived Assets [Line Items]
Asset Impairment Charges						2,000,000
Airbus [Member] | Lease Return Costs
Impaired Long-Lived Assets [Line Items]
Asset Impairment Charges						78,000,000
Q400 [Member]
Impaired Long-Lived Assets [Line Items]
Asset Impairment Charges						$ 61,000,000
Aircraft Permanently Parked | aircraft						2
Aircraft Permanently Parked | aircraft						2
Q400 [Member] | Aircraft [Member]
Impaired Long-Lived Assets [Line Items]
Asset Impairment Charges						$ 58,000,000
Q400 [Member] | Operating Lease Asset
Impaired Long-Lived Assets [Line Items]
Asset Impairment Charges						0
Q400 [Member] | Disposal Group, Held-for-sale, Not Discontinued Operations
Impaired Long-Lived Assets [Line Items]
Asset Impairment Charges						3,000,000
Q400 [Member] | Inventories
Impaired Long-Lived Assets [Line Items]
Asset Impairment Charges						0
Q400 [Member] | Lease Return Costs
Impaired Long-Lived Assets [Line Items]
Asset Impairment Charges						$ 0