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Summary of Significant Accounting Policies - Changes in Accounting Principles (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Changes in Accounting Principles [Abstract]
Aircraft rentals	$ 161	$ 198	$ 229

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- Definition

Changes in Accounting Principles [Abstract]

+ References

No definition available.

+ Details

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

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- Definition

Expenses incurred related to the lease of aircraft from outside third parties that are used in the entity's business operations.

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No definition available.

+ Details

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