| Cover | Oct. 14, 2021 |
| Cover [Abstract] | |
| Document Type | 8-K |
| Amendment Flag | false |
| Document Period End Date | Oct. 14, 2021 |
| Entity File Number | 0-21719 |
| Entity Registrant Name | STEEL DYNAMICS, INC. |
| Entity Central Index Key | 0001022671 |
| Entity Tax Identification Number | 35-1929476 |
| Entity Incorporation, State or Country Code | IN |
| Entity Address, Address Line One | 7575 West Jefferson Blvd |
| Entity Address, City or Town | Fort Wayne |
| Entity Address, State or Province | IN |
| Entity Address, Postal Zip Code | 46804 |
| City Area Code | 260 |
| Local Phone Number | 969-3500 |
| Written Communications | false |
| Soliciting Material | false |
| Pre-commencement Tender Offer | false |
| Pre-commencement Issuer Tender Offer | false |
| Title of 12(b) Security | Common Stock voting, $0.0025 par value |
| Trading Symbol | STLD |
| Security Exchange Name | NASDAQ |
| Entity Emerging Growth Company | false |
