Schedule of Share-based Compensation [Line Items]

No definition available.

Name:	swn_ScheduleOfShareBasedCompensationLineItems
Namespace Prefix:	swn_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Period which an employee's right to exercise liability-based performance units are no longer contingent on satisfaction of either a service condition, market condition or a performance condition, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

+ References

No definition available.

+ Details

Name:	swn_ShareBasedCompensationArrangementAwardLiabilityBasedPerformanceUnitsAwardVestingPeriod
Namespace Prefix:	swn_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Definition

Share-based Compensation Arrangement Award, Liability-based Performance units, Number Of Awards

+ References

No definition available.

+ Details

Name:	swn_ShareBasedCompensationArrangementAwardLiabilityBasedPerformanceUnitsNumberOfAwards
Namespace Prefix:	swn_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	duration

- Definition

The number of liability grants made during the period on other than stock (or unit) option plans (for example, phantom stock or unit plan, stock or unit appreciation rights plan, performance target plan).

+ References

No definition available.

+ Details

Name:	swn_ShareBasedCompensationArrangementByShareBasedPaymentAwardLiabilityInstrumentsOtherThanOptionsGrantsInPeriod
Namespace Prefix:	swn_
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	duration

- Definition

Share-Based Compensation Arrangement By Share-Based Payment Award, Number Unit Types Granted

+ References

No definition available.

+ Details

Name:	swn_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberUnitTypesGranted
Namespace Prefix:	swn_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	instant

- Definition

Amount of cost not yet recognized for nonvested award under share-based payment arrangement.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 718
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Subparagraph (i)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480429/718-10-50-2

+ Details

Name:	us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognized
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Weighted-average period over which cost not yet recognized is expected to be recognized for award under share-based payment arrangement, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents reported fact of one year, five months, and thirteen days.

+ References

+ Details

Name:	us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedPeriodForRecognition1
Namespace Prefix:	us-gaap_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Definition

Amount of cost to be recognized for nonvested award under share-based payment arrangement. Excludes share and unit options.

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 718
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Subparagraph (i)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480429/718-10-50-2

+ Details

Name:	us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedShareBasedAwardsOtherThanOptions
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Estimated period over which an employee is required to provide service in exchange for the equity-based payment award, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

+ References

Reference 1: http://www.xbrl.org/2003/role/exampleRef
-Topic 718
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Subparagraph (a)(1)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480429/718-10-50-2

+ Details

Name:	us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardAwardRequisiteServicePeriod1
Namespace Prefix:	us-gaap_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Definition

Period over which grantee's right to exercise award under share-based payment arrangement is no longer contingent on satisfaction of service or performance condition, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents reported fact of one year, five months, and thirteen days. Includes, but is not limited to, combination of market, performance or service condition.

+ References

+ Details

Name:	us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardAwardVestingPeriod1
Namespace Prefix:	us-gaap_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Definition

The number of grants made during the period on other than stock (or unit) option plans (for example, phantom stock or unit plan, stock or unit appreciation rights plan, performance target plan).

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 718
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Subparagraph (c)(2)(iii)(01)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480429/718-10-50-2

+ Details

Name:	us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod
Namespace Prefix:	us-gaap_
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	duration

- Definition

Number of equity instruments other than options outstanding, including both vested and non-vested instruments.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Subparagraph (c)(1)(i)
-SubTopic 10
-Topic 718
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480429/718-10-50-2

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Subparagraph (c)(1)(ii)
-SubTopic 10
-Topic 718
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480429/718-10-50-2

+ Details

Name:	us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNonOptionEquityInstrumentsOutstandingNumber
Namespace Prefix:	us-gaap_
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	instant

- Definition

Period from grant date that an equity-based award expires, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

+ References

Reference 1: http://www.xbrl.org/2003/role/exampleRef
-Topic 718
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Subparagraph (a)(2)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480429/718-10-50-2

+ Details

Name:	us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardExpirationPeriod
Namespace Prefix:	us-gaap_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Details

Name:	us-gaap_PlanNameAxis=swn_StockBasedCompensation2022PlanMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_AwardTypeAxis=us-gaap_EmployeeStockOptionMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_AwardTypeAxis=us-gaap_RestrictedStockMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_AwardTypeAxis=us-gaap_PerformanceSharesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_AwardDateAxis=swn_AwardsGranted20222023Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_AwardTypeAxis=swn_EquityClassifiedRestrictedStockUnitsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_AwardTypeAxis=swn_LiabilityClassifiedRestrictedStockUnitsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_AwardTypeAxis=swn_LiabilityClassifiedPerformanceUnitsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_AwardTypeAxis=swn_RestrictedCashUnitsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_AwardDateAxis=swn_AwardsGranted20202022Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_AwardDateAxis=swn_AwardsGranted20232024Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

LONG-TERM INCENTIVE COMPENSATION - Narrative (Details) $ in Millions	3 Months Ended	12 Months Ended				72 Months Ended
	Mar. 31, 2024 USD ($) share_unit_type shares	Dec. 31, 2023 awardType	Dec. 31, 2022 awardType	Dec. 31, 2021 awardType	Dec. 31, 2020	Dec. 31, 2023
Stock Based Compensation 2022 Plan
Schedule of Share-based Compensation [Line Items]
Service period	3 years
Unexercised stock options
Schedule of Share-based Compensation [Line Items]
Vesting period	3 years
Expiration period	10 years
Restricted stock
Schedule of Share-based Compensation [Line Items]
Vesting period	3 years
Granted (in shares)	0
Equity-classified awards, unrecognized compensation cost \| $	$ 1
Employee service share-based compensation, nonvested awards, compensation cost not yet recognized, period for recognition	1 month 6 days
Performance units
Schedule of Share-based Compensation [Line Items]
Vesting period	3 years	3 years	3 years	3 years		3 years
Granted (in shares)	0
Equity-classified awards, unrecognized compensation cost \| $	$ 5
Employee service share-based compensation, nonvested awards, compensation cost not yet recognized, period for recognition	1 year 7 months 6 days
Share-Based Compensation Arrangement by Share-Based Payment Award, Non-Option Equity Instruments, Outstanding, Number	0
Performance units \| Awards Granted 2022 - 2023
Schedule of Share-based Compensation [Line Items]
Number of performance unit types granted \| share_unit_type	2
Equity-Classified Restricted Stock Units
Schedule of Share-based Compensation [Line Items]
Granted (in shares)	3,182,000
Equity-classified awards, unrecognized compensation cost \| $	$ 20
Employee service share-based compensation, nonvested awards, compensation cost not yet recognized, period for recognition	2 years 4 months 24 days
Liability-Classified Restricted Stock Units
Schedule of Share-based Compensation [Line Items]
Vesting period				3 years		4 years
Granted (in shares)	0
Liability-Classified Performance Units
Schedule of Share-based Compensation [Line Items]
Vesting period						3 years
Employee service share-based compensation, nonvested awards, compensation cost not yet recognized, period for recognition	1 year 9 months 18 days
Liability classified awards, unrecognized compensation costs \| $	$ 3
Liability-classified performance units, vesting period		3 years	3 years	3 years	3 years
Number of awards \| awardType		2	2	2
Granted (in shares)	0
Performance cash awards
Schedule of Share-based Compensation [Line Items]
Employee service share-based compensation, nonvested awards, compensation cost not yet recognized, period for recognition	2 years 3 months 18 days
Liability classified awards, unrecognized compensation costs \| $	$ 54
Granted (in shares)	28,202,000
Performance cash awards \| Awards Granted 2020 - 2022
Schedule of Share-based Compensation [Line Items]
Vesting period				4 years
Performance cash awards \| Awards Granted 2023 - 2024
Schedule of Share-based Compensation [Line Items]
Vesting period	3 years