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Stock-Based Compensation (Schedule Of Stock-Based Compensation Costs - Equity-Classified Performance Units) (Details) (Equity-Classified Performance Units [Member], USD $)
In Millions, unless otherwise specified
 12 Months Ended
Dec. 31, 2014
Equity-Classified Performance Units [Member]
  
Stock-based compensation costs - expensed $ 3us-gaap_AllocatedShareBasedCompensationExpense
/ us-gaap_AwardTypeAxis
= swn_EquityClassifiedPerformanceUnitsMember
Stock-based compensation costs - capitalized $ 2us-gaap_EmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsCapitalizedAmount
/ us-gaap_AwardTypeAxis
= swn_EquityClassifiedPerformanceUnitsMember