Debt Instrument, Covenant Compliance, Limit Of Securing Indebtedness

No definition available.

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

- Definition

Debt Instrument, Covenant Compliance, Limit Of Securing Indebtedness, Amount

+ References

No definition available.

+ Details

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

- Definition

Debt Instrument, Covenant Compliance, Limit Of Securing Indebtedness, Percentage Of Consolidated Net Tangible Assets

+ References

No definition available.

+ Details

Name:	swn_DebtInstrumentCovenantComplianceLimitOfSecuringIndebtednessPercentageOfConsolidatedNetTangibleAssets
Namespace Prefix:	swn_
Data Type:	dtr-types:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Total debt divided by EBITDAX.

+ References

No definition available.

+ Details

Name:	swn_LeverageRatio
Namespace Prefix:	swn_
Data Type:	xbrli:pureItemType
Balance Type:	na
Period Type:	duration

- Definition

Leverage Ratio, Amount of Credit Limit

+ References

No definition available.

+ Details

Name:	swn_LeverageRatioAmountOfCreditLimit
Namespace Prefix:	swn_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Leverage Ratio, Percentage of Credit Limit

+ References

No definition available.

+ Details

Name:	swn_LeverageRatioPercentageOfCreditLimit
Namespace Prefix:	swn_
Data Type:	dtr-types:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Long-Term Debt, Excluding Maturities, Gross

+ References

No definition available.

+ Details

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

- Definition

EBITDAX divided by consolidated interest expense.

+ References

No definition available.

+ Details

Name:	swn_MinimumInterestCoverageRatio
Namespace Prefix:	swn_
Data Type:	xbrli:pureItemType
Balance Type:	na
Period Type:	duration

- Definition

Percentage points added to the reference rate to compute the variable rate on the debt instrument.

+ References

No definition available.

+ Details

Name:	us-gaap_DebtInstrumentBasisSpreadOnVariableRate1
Namespace Prefix:	us-gaap_
Data Type:	dtr-types:percentItemType
Balance Type:	na
Period Type:	duration

- 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

The total amount of the contingent obligation under letters of credit outstanding as of the reporting date.

+ References

No definition available.

+ Details

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

- Definition

The carrying value as of the balance sheet date of the current and noncurrent portions of long-term obligations drawn from a line of credit, which is a bank's commitment to make loans up to a specific amount. Examples of items that might be included in the application of this element may consist of letters of credit, standby letters of credit, and revolving credit arrangements, under which borrowings can be made up to a maximum amount as of any point in time conditional on satisfaction of specified terms before, as of and after the date of drawdowns on the line. Includes short-term obligations that would normally be classified as current liabilities but for which (a) postbalance sheet date issuance of a long term obligation to refinance the short term obligation on a long term basis, or (b) the enterprise has entered into a financing agreement that clearly permits the enterprise to refinance the short-term obligation on a long term basis and the following conditions are met (1) the agreement does not expire within 1 year and is not cancelable by the lender except for violation of an objectively determinable provision, (2) no violation exists at the BS date, and (3) the lender has entered into the financing agreement is expected to be financially capable of honoring the agreement.

+ 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(22))
-URI http://asc.fasb.org/extlink&oid=120391452&loc=d3e13212-122682

Reference 2: 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=120398452&loc=d3e534808-122878

Reference 3: 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=120400017&loc=d3e572229-122910

+ Details

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

- Definition

Amount of current borrowing capacity under the credit facility considering any current restrictions on the amount that could be borrowed (for example, borrowings may be limited by the amount of current assets), but without considering any amounts currently outstanding under the facility.

+ References

+ Details

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

- Definition

Maximum borrowing capacity under the credit facility without consideration of any current restrictions on the amount that could be borrowed or the amounts currently outstanding under the facility.

+ References

+ Details

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

- Definition

Percentage of subsidiary's or equity method investee's stock owned by parent immediately after all stock transactions.

+ References

No definition available.

+ Details

Name:	us-gaap_SubsidiaryOrEquityMethodInvesteeCumulativePercentageOwnershipAfterAllTransactions
Namespace Prefix:	us-gaap_
Data Type:	dtr-types:percentItemType
Balance Type:	na
Period Type:	duration

- Details

Name:	us-gaap_LongtermDebtTypeAxis=us-gaap_LongTermDebtMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_CreditFacilityAxis=swn_CreditFacilityFourMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_RangeAxis=srt_MaximumMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_VariableRateAxis=us-gaap_EurodollarMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_RangeAxis=srt_MinimumMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_VariableRateAxis=us-gaap_BaseRateMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_LongtermDebtTypeAxis=us-gaap_LineOfCreditMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_CreditFacilityAxis=us-gaap_RevolvingCreditFacilityMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DebtInstrumentAxis=swn_A2018RevolvingCreditFacilityMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	swn_DebtInstrumentCovenantCompliancePeriodOfComplianceAxis=swn_AfterJune302020Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Debt (2018 Revolving Credit Facility - Narrative) (Details)	1 Months Ended	3 Months Ended	9 Months Ended
	Apr. 30, 2018 USD ($)	Jun. 30, 2018 USD ($)	Sep. 30, 2021 USD ($)	Dec. 31, 2020 USD ($)
Debt Instrument [Line Items]
Subsidiary ownership			100.00%
Letters of credit			$ 159,000,000
Long-term debt, excluding maturity, gross				$ 3,171,000,000
Long-term debt
Debt Instrument [Line Items]
Long-term debt, excluding maturity, gross			4,044,000,000
Long-term debt \| 2018 revolving credit facility due April 2024
Debt Instrument [Line Items]
Maximum borrowing capacity	$ 3,500,000,000
Current borrowing base			2,000,000,000
Aggregate commitment			2,000,000,000
Limit on securing indebtedness	$ 2,000,000,000
Percentage of consolidated net tangible assets	25.00%
Debt instrument, covenant compliance, limit of securing indebtedness, amount	$ 2,900,000,000
Minimum interest coverage ratio		1.00
Long-term debt \| 2018 revolving credit facility due April 2024 \| Maximum
Debt Instrument [Line Items]
Leverage ratio, percentage of credit limit		10.00%
Leverage ratio, amount of credit limit		$ 150,000,000
Long-term debt \| 2018 revolving credit facility due April 2024 \| Eurodollar \| Minimum
Debt Instrument [Line Items]
Basis points	1.75%
Long-term debt \| 2018 revolving credit facility due April 2024 \| Eurodollar \| Maximum
Debt Instrument [Line Items]
Basis points	2.75%
Long-term debt \| 2018 revolving credit facility due April 2024 \| Base Rate \| Minimum
Debt Instrument [Line Items]
Basis points	0.75%
Long-term debt \| 2018 revolving credit facility due April 2024 \| Base Rate \| Maximum
Debt Instrument [Line Items]
Basis points	1.75%
Line of Credit \| Revolving Credit Facility \| 2018 Revolving Credit Facility
Debt Instrument [Line Items]
Long-term debt, excluding maturity, gross			$ 665,000,000
After June 30, 2020 \| Long-term debt \| 2018 revolving credit facility due April 2024 \| Maximum
Debt Instrument [Line Items]
Leverage ratio		4.00