Commitments and Contingencies - Airport Projects (Details) - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Airport Project
ACFO	$ 309	$ 164
Depreciation and amortization	1,255	1,219	$ 1,201
Construction obligation	309	164
LosAngelesWorldAirportTerminal1.5 [Member]
Airport Project
Expected total airport modernization project cost	464
Contractual Obligation	318
DAL [Member]
Airport Project
Municipal Bonds Principal Remaining	399
Net Present Value of Principal Remaining	$ 433	$ 444

[Line Items] for Airport Project [Table]

No definition available.

Name:	luv_AirportProjectLineItems
Namespace Prefix:	luv_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

The aggregate costs related to airport construction projects recorded as an asset.

+ References

No definition available.

+ Details

Name:	luv_AssetsConstructedForOthers
Namespace Prefix:	luv_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Construction Obligation, Noncurrent

+ References

No definition available.

+ Details

Name:	luv_ConstructionObligationNoncurrent
Namespace Prefix:	luv_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

The total expected cost of the airport modernization project for the city.

+ References

No definition available.

+ Details

Name:	luv_ExpectedTotalCostOfAirportProject
Namespace Prefix:	luv_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Municipal Bonds Principal Remaining

+ References

No definition available.

+ Details

Name:	luv_MunicipalBondsPrincipalRemaining
Namespace Prefix:	luv_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Net Present Value of Principal Remaining

+ References

No definition available.

+ Details

Name:	luv_NetPresentValueofPrincipalRemaining
Namespace Prefix:	luv_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Amount of contractual obligation, including but not limited to, long-term debt, capital lease obligations, operating lease obligations, purchase obligations, and other commitments.

+ References

No definition available.

+ Details

Name:	us-gaap_ContractualObligation
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

The current period expense charged against earnings on long-lived, physical assets not used in production, and which are not intended for resale, to allocate or recognize the cost of such assets over their useful lives; or to record the reduction in book value of an intangible asset over the benefit period of such asset; or to reflect consumption during the period of an asset that is not used in production.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 360
-SubTopic 10
-Section 50
-Paragraph 1
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=6391035&loc=d3e2868-110229

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 28
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=121586364&loc=d3e3602-108585

+ Details

Name:	us-gaap_DepreciationAndAmortization
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Details

Name:	luv_AirportProjectAxis=luv_LosAngelesWorldAirportTerminal1.5Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	luv_AirportProjectAxis=luv_DALMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: