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Fair Value Measurements (Narrative) (Details)
 12 Months Ended
Dec. 31, 2014
Dec. 31, 2013
7.5% Senior Notes Due 2018 [Member]    
Debt Instrument [Line Items]    
Debt instrument, interest rate, stated percentage 7.50%us-gaap_DebtInstrumentInterestRateStatedPercentage
/ us-gaap_DebtInstrumentAxis
= swn_SeniorNotes75Due2018Member		  
Yield, Publicly-traded debt market 3.20%swn_YeildPubliclyTradedDebtMarket
/ us-gaap_DebtInstrumentAxis
= swn_SeniorNotes75Due2018Member		 2.60%swn_YeildPubliclyTradedDebtMarket
/ us-gaap_DebtInstrumentAxis
= swn_SeniorNotes75Due2018Member
Debt Instrument, Maturity Year 2018  
4.10% Senior Notes Due 2022 [Member]    
Debt Instrument [Line Items]    
Debt instrument, interest rate, stated percentage 4.10%us-gaap_DebtInstrumentInterestRateStatedPercentage
/ us-gaap_DebtInstrumentAxis
= swn_SeniorNotes410Due2022Member		  
Yield, Publicly-traded debt market 4.30%swn_YeildPubliclyTradedDebtMarket
/ us-gaap_DebtInstrumentAxis
= swn_SeniorNotes410Due2022Member		 4.20%swn_YeildPubliclyTradedDebtMarket
/ us-gaap_DebtInstrumentAxis
= swn_SeniorNotes410Due2022Member
Debt Instrument, Maturity Year 2022