| Cover | Jan. 20, 2021 |
| Cover [Abstract] | |
| Document Type | 8-K |
| Document Period End Date | Jan. 20, 2021 |
| Entity Registrant Name | MURPHY USA INC. |
| Entity Incorporation, State or Country Code | DE |
| Entity File Number | 001-35914 |
| Entity Tax Identification Number | 46-2279221 |
| Entity Address, Address Line One | 200 Peach Street |
| Entity Address, Postal Zip Code | 71730-5836 |
| City Area Code | 870 |
| Local Phone Number | 875-7600 |
| 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 | MUSA |
| Security Exchange Name | NYSE |
| Entity Emerging Growth Company | false |
| Entity Central Index Key | 0001573516 |
| Amendment Flag | false |
| Entity Address, City or Town | El Dorado |
| Entity Address, State or Province | AR |
