| Cover page Cover page | Feb. 17, 2021 |
| Cover [Abstract] | |
| Document Type | 8-K |
| Document Period End Date | Feb. 17, 2021 |
| Entity Registrant Name | SM Energy Co |
| Entity Incorporation, State or Country Code | DE |
| Entity File Number | 001-31539 |
| Entity Tax Identification Number | 41-0518430 |
| Entity Address, Address Line One | 1775 Sherman Street, Suite 1200, |
| Entity Address, City or Town | Denver |
| Entity Address, State or Province | CO |
| Entity Address, Postal Zip Code | 80203 |
| City Area Code | (303) |
| Local Phone Number | 861-8140 |
| Written Communications | false |
| Soliciting Material | false |
| Pre-commencement Tender Offer | false |
| Pre-commencement Issuer Tender Offer | false |
| Title of 12(b) Security | Common stock, $0.01 par value |
| Trading Symbol | SM |
| Security Exchange Name | NYSE |
| Entity Emerging Growth Company | false |
| Entity Central Index Key | 0000893538 |
| Amendment Flag | false |
