Fair Value Instruments - Carrying and Estimated Fair Value of Debt (Details) $ in Millions	Mar. 31, 2020 USD ($)
2.65% Notes due 2020 \| Unsecured Debt
Debt Instrument [Line Items]
Carrying amount of debt	$ 504
Stated interest rate	2.65%
Term Loan Agreement payable through 2020 - 5.223% \| Notes Payable to Banks
Debt Instrument [Line Items]
Carrying amount of debt	$ 120
Stated interest rate	5.223%
737 Aircraft Notes payable through 2020 \| Notes Payable to Banks
Debt Instrument [Line Items]
Carrying amount of debt	$ 7
2.75% Notes due 2022 \| Unsecured Debt
Debt Instrument [Line Items]
Carrying amount of debt	$ 300
Stated interest rate	2.75%
Pass Through Certificates due 2022 - 6.24% \| Enhanced Equipment Trust Certificate
Debt Instrument [Line Items]
Carrying amount of debt	$ 168
Stated interest rate	6.24%
Term Loan Agreement due 2026 - 3.71% \| Notes Payable to Banks
Debt Instrument [Line Items]
Carrying amount of debt	$ 178
Stated interest rate	3.03%
3.00% Notes due 2026 \| Unsecured Debt
Debt Instrument [Line Items]
Carrying amount of debt	$ 300
Stated interest rate	3.00%
3.45% Notes due 2027 \| Unsecured Debt
Debt Instrument [Line Items]
Carrying amount of debt	$ 300
Stated interest rate	3.45%
7.375% Debentures due 2027 \| Unsecured Debt
Debt Instrument [Line Items]
Carrying amount of debt	$ 121
Stated interest rate	7.375%
2.625% Notes due 2030
Debt Instrument [Line Items]
Stated interest rate	2.625%
2.625% Notes due 2030 \| Unsecured Debt
Debt Instrument [Line Items]
Carrying amount of debt	$ 500
Stated interest rate	2.625%
Level 2 \| 2.65% Notes due 2020 \| Unsecured Debt
Debt Instrument [Line Items]
Notes Payable, Fair Value	$ 495
Level 2 \| 2.75% Notes due 2022 \| Unsecured Debt
Debt Instrument [Line Items]
Notes Payable, Fair Value	283
Level 2 \| Pass Through Certificates due 2022 - 6.24% \| Enhanced Equipment Trust Certificate
Debt Instrument [Line Items]
Notes Payable, Fair Value	167
Level 2 \| 3.00% Notes due 2026 \| Unsecured Debt
Debt Instrument [Line Items]
Notes Payable, Fair Value	284
Level 2 \| 3.45% Notes due 2027 \| Unsecured Debt
Debt Instrument [Line Items]
Notes Payable, Fair Value	264
Level 2 \| 7.375% Debentures due 2027 \| Unsecured Debt
Debt Instrument [Line Items]
Loans Payable, Fair Value	139
Level 2 \| 2.625% Notes due 2030 \| Unsecured Debt
Debt Instrument [Line Items]
Notes Payable, Fair Value	420
Level 3 \| Term Loan Agreement payable through 2020 - 5.223% \| Notes Payable to Banks
Debt Instrument [Line Items]
Loans Payable, Fair Value	120
Level 3 \| 737 Aircraft Notes payable through 2020 \| Notes Payable to Banks
Debt Instrument [Line Items]
Notes Payable, Fair Value	7
Level 3 \| Term Loan Agreement Due 2021 \| Notes Payable to Banks
Debt Instrument [Line Items]
Loans Payable, Fair Value	990
Level 3 \| Term Loan Agreement due 2026 - 3.71% \| Notes Payable to Banks
Debt Instrument [Line Items]
Loans Payable, Fair Value	$ 164
Notes Payable to Banks \| Term Loan Agreement Due 2021
Debt Instrument [Line Items]
Stated interest rate	3.00%
Short-term Debt	$ 1,000
Revolving Credit Facility
Debt Instrument [Line Items]
Revolving Credit Facility, Maximum Amount Outstanding at Period End	1,000
Revolving Credit Facility \| Level 3
Debt Instrument [Line Items]
Line of Credit Facility, Fair Value	$ 978

Line of Credit Facility, Maximum Amount Outstanding at Period End

No definition available.

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

- Definition

Amount, before unamortized (discount) premium and debt issuance costs, of long-term debt. Includes, but is not limited to, notes payable, bonds payable, commercial loans, mortgage loans, convertible debt, subordinated debt and other types of debt.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 470
-SubTopic 20
-Section 50
-Paragraph 4
-Subparagraph (b)(1)
-URI http://asc.fasb.org/extlink&oid=109500613&loc=SL6031897-161870

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.7-03(16))
-URI http://asc.fasb.org/extlink&oid=119400593&loc=d3e572229-122910

Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02(22))
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

Reference 4: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-03(16))
-URI http://asc.fasb.org/extlink&oid=6876686&loc=d3e534808-122878

+ Details

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

- Definition

Contractual interest rate for funds borrowed, under the debt agreement.

+ References

+ Details

Name:	us-gaap_DebtInstrumentInterestRateStatedPercentage
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

No definition available.

+ Details

Name:	us-gaap_DebtInstrumentLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Fair value of the amount outstanding under the credit facility.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 825
-SubTopic 10
-Section 50
-Paragraph 10
-URI http://asc.fasb.org/extlink&oid=118260190&loc=d3e13433-108611

+ Details

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

- Definition

Fair value portion of contractual obligation to pay money on demand or on fixed or determinable dates.

+ References

No definition available.

+ Details

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

- Definition

Fair value portion of notes payable.

+ References

+ Details

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

- Definition

Reflects the total carrying amount as of the balance sheet date of debt having initial terms less than one year or the normal operating cycle, if longer.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02(19)(a))
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.7-03(a)(16)(a)(1))
-URI http://asc.fasb.org/extlink&oid=119400593&loc=d3e572229-122910

Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-03(13))
-URI http://asc.fasb.org/extlink&oid=6876686&loc=d3e534808-122878

+ Details

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Balance Type:	credit
Period Type:	instant