| Document and Entity Information | Aug. 16, 2021 |
| Cover [Abstract] | |
| Entity Registrant Name | SOUTHWESTERN ENERGY CO |
| Amendment Flag | false |
| Entity Central Index Key | 0000007332 |
| Document Type | 8-K |
| Document Period End Date | Aug. 16, 2021 |
| Entity Incorporation State Country Code | DE |
| Entity File Number | 001-08246 |
| Entity Tax Identification Number | 71-0205415 |
| Entity Address, Address Line One | 10000 Energy Drive |
| Entity Address, City or Town | Spring |
| Entity Address, State or Province | TX |
| Entity Address, Postal Zip Code | 77389 |
| City Area Code | (832) |
| Local Phone Number | 796-1000 |
| Written Communications | false |
| Soliciting Material | false |
| Pre Commencement Tender Offer | false |
| Pre Commencement Issuer Tender Offer | false |
| Security 12b Title | Common Stock, Par Value $0.01 |
| Trading Symbol | SWN |
| Security Exchange Name | NYSE |
| Entity Emerging Growth Company | false |
