Cover page - USD ($)	12 Months Ended
	Dec. 31, 2021	Feb. 10, 2022	Jun. 30, 2021
Cover [Abstract]
Document Type	10-K
Document Annual Report	true
Document Period End Date	Dec. 31, 2021
Document Transition Report	false
Entity File Number	001-31539
Entity Registrant Name	SM ENERGY CO
Entity Incorporation, State or Country Code	DE
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
Title of 12(b) Security	Common stock, $.01 par value
Trading Symbol	SM
Security Exchange Name	NYSE
Entity Well-known Seasoned Issuer	Yes
Entity Voluntary Filers	No
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity Filer Category	Large Accelerated Filer
Entity Small Business	false
Entity Emerging Growth Company	false
ICFR Auditor Attestation Flag	true
Entity Shell Company	false
Entity Public Float			$ 2,939,253,438
Entity Common Stock, Shares Outstanding		121,862,248
Documents Incorporated by Reference	Certain information required by Items 10, 11, 12, 13, and 14 of Part III of this report is incorporated by reference from portions of the registrant’s Definitive Proxy Statement on Schedule 14A relating to its 2022 annual meeting of stockholders, to be filed within 120 days after December 31, 2021.
Entity Central Index Key	0000893538
Current Fiscal Year End Date	--12-31
Document Fiscal Year Focus	2021
Document Fiscal Period Focus	FY
Amendment Flag	false