Document and Entity Information (USD $)	12 Months Ended
	Dec. 31, 2012	Jun. 29, 2012	Feb. 15, 2012
Document And Entity Information [Abstract]
Document Type	10-K
Amendment Flag	false
Document Period End Date	Dec. 31, 2012
Document Fiscal Year Focus	2012
Document Fiscal Period Focus	FY
Entity Registrant Name	Southwestern Energy Co
Entity Central Index Key	0000007332
Current Fiscal Year End Date	--12-31
Entity Filer Category	Large Accelerated Filer
Entity Common Stock, Shares Outstanding			351,097,392
Entity Well-known Seasoned Issuer	Yes
Entity Voluntary Filers	No
Entity Current Reporting Status	Yes
Entity Public Float		$ 10,933,390,189
Trading Symbol	SWN