Commitments and Contingencies (Narrative) (Details)	Jun. 12, 2018 individual company	Dec. 31, 2021 USD ($) lease
Commitments And Contingencies [Line Items]
Obligation under transportation agreements		$ 10,456,000,000
Guarantee obligations relative to the firms transportation agreements and gathering project and services		869,000,000
Maturities of operating leases (ASC 842):
2022		53,000,000
2023		42,000,000
2024		31,000,000
2025		28,000,000
2026		25,000,000
Thereafter		42,000,000
Number of plaintiffs \| individual	51
Number of defendants \| company	15
Indemnification liability		0
Pending regulatory approval and/or construction
Commitments And Contingencies [Line Items]
Obligation under transportation agreements		872,000,000
Indigo Agreement
Commitments And Contingencies [Line Items]
Obligation under transportation agreements		36,000,000
Liability for the estimated future payments		17,000,000
Purchase or volume commitments with gathering fresh water and sand
Commitments And Contingencies [Line Items]
Obligation under transportation agreements		74,000,000
Appalachian Basin
Commitments And Contingencies [Line Items]
Obligation under transportation agreements		327,000,000
Maturities of operating leases (ASC 842):
Obligation under transportation agreements, reimbursed by seller		100,000,000
Pressure Pumping Equipment \| Exploration and Production
Commitments And Contingencies [Line Items]
Aggregate annual lease payment		7,000,000
Drilling Rigs \| Exploration and Production
Commitments And Contingencies [Line Items]
Aggregate annual lease payment		$ 10,000,000
Number of leases \| lease		7
Office Space, Vehicles And Equipment
Maturities of operating leases (ASC 842):
2022		$ 38,000,000
2023		34,000,000
2024		27,000,000
2025		26,000,000
2026		24,000,000
Thereafter		38,000,000
Compression Rentals
Maturities of operating leases (ASC 842):
2022		24,000,000
2023		10,000,000
2024		4,000,000
2025		$ 1,000,000

Aggregate Annual Lease Payment

No definition available.

Name:	swn_AggregateAnnualLeasePayment
Namespace Prefix:	swn_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Commitments And Contingencies [Line Items]

+ References

No definition available.

+ Details

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

- Definition

Liability Associated With Indemnification Obligation

+ References

No definition available.

+ Details

Name:	swn_LiabilityAssociatedWithIndemnificationObligation
Namespace Prefix:	swn_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Other Commitment, Reimbursed By Seller

+ References

No definition available.

+ Details

Name:	swn_OtherCommitmentReimbursedBySeller
Namespace Prefix:	swn_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Other Commitment, to be Paid

+ References

No definition available.

+ Details

Name:	swn_OtherCommitmentToBePaid
Namespace Prefix:	swn_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

The current carrying amount of the liability for the freestanding or embedded guarantor's obligations under the guarantee or each group of similar guarantees.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 460
-SubTopic 10
-Section 50
-Paragraph 4
-Subparagraph (c)
-URI http://asc.fasb.org/extlink&oid=124440162&loc=d3e12069-110248

+ Details

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

- Definition

Amount of lessee's undiscounted obligation for lease payment for operating lease due after fifth fiscal year following current fiscal year. Excludes interim and annual periods when interim periods are reported from current statement of financial position date (rolling approach).

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 842
-SubTopic 20
-Section 50
-Paragraph 6
-URI http://asc.fasb.org/extlink&oid=123408670&loc=SL77918701-209980

+ Details

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

- Definition

Amount of lessee's undiscounted obligation for lease payment for operating lease to be paid in next fiscal year following current fiscal year. Excludes interim and annual periods when interim periods are reported from current statement of financial position date (rolling approach).

+ References

+ Details

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

- Definition

Amount of lessee's undiscounted obligation for lease payment for operating lease to be paid in fifth fiscal year following current fiscal year. Excludes interim and annual periods when interim periods are reported from current statement of financial position date (rolling approach).

+ References

+ Details

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

- Definition

Amount of lessee's undiscounted obligation for lease payment for operating lease to be paid in fourth fiscal year following current fiscal year. Excludes interim and annual periods when interim periods are reported from current statement of financial position date (rolling approach).

+ References

+ Details

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

- Definition

Amount of lessee's undiscounted obligation for lease payment for operating lease to be paid in third fiscal year following current fiscal year. Excludes interim and annual periods when interim periods are reported from current statement of financial position date (rolling approach).

+ References

+ Details

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

- Definition

Amount of lessee's undiscounted obligation for lease payment for operating lease to be paid in second fiscal year following current fiscal year. Excludes interim and annual periods when interim periods are reported from current statement of financial position date (rolling approach).

+ References

+ Details

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

- Definition

Number of defendants named in a legal action.

+ References

No definition available.

+ Details

Name:	us-gaap_LossContingencyNumberOfDefendants
Namespace Prefix:	us-gaap_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	duration

- Definition

Number of plaintiffs that have filed claims pertaining to a loss contingency.

+ References

No definition available.

+ Details

Name:	us-gaap_LossContingencyNumberOfPlaintiffs
Namespace Prefix:	us-gaap_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	duration

- Definition

Number of separate real estate development properties located on land subject to ground leases.

+ References

No definition available.

+ Details

Name:	us-gaap_NumberOfPropertiesSubjectToGroundLeases
Namespace Prefix:	us-gaap_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	instant

- References

No definition available.

+ Details

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

- Definition

Minimum amount of other commitment not otherwise specified in the taxonomy. Excludes commitments explicitly modeled in the taxonomy, including but not limited to, long-term and short-term purchase commitments, recorded and unrecorded purchase obligations, supply commitments, registration payment arrangements, leases, debt, product warranties, guarantees, environmental remediation obligations, and pensions.

+ References

No definition available.

+ Details

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

- Details

Name:	us-gaap_OtherCommitmentsAxis=swn_PendingRegulatoryApprovalAndOrConstructionMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_OtherCommitmentsAxis=swn_IndigoAgreementMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_OtherCommitmentsAxis=swn_PurchaseOrVolumeCommitmentsWithGatheringFreshWaterAndSandMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_StatementGeographicalAxis=swn_AppalachianBasinMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_PropertyPlantAndEquipmentByTypeAxis=swn_PressurePumpingEquipmentMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_StatementBusinessSegmentsAxis=swn_ExplorationAndProductionReportableSegmentMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_PropertyPlantAndEquipmentByTypeAxis=swn_DrillingRigsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_PropertyPlantAndEquipmentByTypeAxis=swn_OfficeSpaceVehiclesAndEquipmentMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_PropertyPlantAndEquipmentByTypeAxis=swn_CompressionRentalsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: