LEASES - Narrative (Details)	3 Months Ended								6 Months Ended		9 Months Ended	12 Months Ended
LEASES - Narrative (Details)	Mar. 31, 2025 USD ($) aircraft	Dec. 31, 2024 USD ($) aircraft	Mar. 31, 2024 USD ($)	Dec. 31, 2023 USD ($)	Sep. 30, 2023 USD ($)	Jun. 30, 2023 USD ($)	Mar. 31, 2023 USD ($) aircraft	Dec. 31, 2022 aircraft	Mar. 31, 2025 USD ($) aircraft	Sep. 30, 2023 aircraft	Dec. 31, 2023 USD ($)	Dec. 31, 2025 USD ($)	Dec. 31, 2024 USD ($) aircraft airframe	Dec. 31, 2023 USD ($)
Lessee, Lease, Description [Line Items]
Other operating expenses												$ 4,467,000,000	$ 4,138,000,000	$ 3,999,000,000
Gain on sale-leaseback transactions												3,000,000	92,000,000	0
Operating lease right-of-use assets		$ 1,369,000,000										1,089,000,000	1,369,000,000
Operating lease, liability												1,080,000,000
Capital expenditures												2,673,000,000	2,054,000,000	3,520,000,000
Payments of long-term debt and finance lease obligations												3,275,000,000	1,337,000,000	85,000,000
Total lease obligations		91,000,000										78,000,000	91,000,000
Aircraft
Lessee, Lease, Description [Line Items]
Other operating expenses												$ 33,000,000	0	0
Capital expenditures													45,000,000
Payments of long-term debt and finance lease obligations													3,000,000
Payments of long-term debt and operating lease obligations													2,000,000
Total lease obligations		$ 40,000,000											40,000,000
Gain (loss) on termination of lease													$ 0
Number of leased aircrafts, operating lease \| aircraft		82											82
Number of leased aircrafts, finance lease \| aircraft		15											15
Aircraft \| Boeing 737-800
Lessee, Lease, Description [Line Items]
Number of aircraft sale agreements \| aircraft		36
Number of aircrafts sold \| aircraft	1	35
Proceeds from sale of property, plant, and equipment	$ 24,000,000	$ 871,000,000
Sale leaseback transaction, lease term (in years)	3 years
Number of aircrafts de-recognized \| aircraft									36
Gain on sale-leaseback transactions	$ 3,000,000	92,000,000
Operating lease right-of-use assets	9,000,000	319,000,000							$ 9,000,000				$ 319,000,000
Operating lease, liability	$ 9,000,000	$ 319,000,000							$ 9,000,000				$ 319,000,000
Number of aircraft purchase agreements \| aircraft													1
Number of airframe purchase agreements \| airframe													1
Aircraft \| Boeing 737-700
Lessee, Lease, Description [Line Items]
Number of aircraft purchase agreements \| aircraft							39			4			2
Capital expenditures							$ 88,000,000				$ 44,000,000
Payments of long-term debt and finance lease obligations							50,000,000				3,000,000
Total lease obligations				$ 41,000,000			$ 38,000,000				$ 41,000,000			$ 41,000,000
Gain (loss) on termination of lease			$ 0	$ 0	$ 0	$ 0
Number of aircrafts purchased \| aircraft							8	31
Airport-Related
Lessee, Lease, Description [Line Items]
Term of lease contract (in years)												35 years
Maximum \| Aircraft
Lessee, Lease, Description [Line Items]
Term of contract (in years)												8 years
Renewal term (in years)												3 years
Maximum \| Aircraft \| Boeing 737-800
Lessee, Lease, Description [Line Items]
Sale leaseback transaction, lease term (in years)		3 years
Maximum \| Airport-Related
Lessee, Lease, Description [Line Items]
Renewal term (in years)												11 years
Maximum \| Other
Lessee, Lease, Description [Line Items]
Term of contract (in years)												5 years
Renewal term (in years)												1 year
Minimum \| Aircraft
Lessee, Lease, Description [Line Items]
Renewal term (in years)												3 months
Minimum \| Aircraft \| Boeing 737-800
Lessee, Lease, Description [Line Items]
Sale leaseback transaction, lease term (in years)		2 years
Minimum \| Airport-Related
Lessee, Lease, Description [Line Items]
Renewal term (in years)												1 year

SOUTHWEST AIRLINES CO 10-K