| Cover | Nov. 03, 2022 |
| Entity Information [Line Items] | |
| Document Type | 8-K |
| Document Period End Date | Nov. 03, 2022 |
| Entity Registrant Name | MP Materials Corp. / DE |
| Entity Incorporation, State or Country Code | DE |
| Entity File Number | 001-39277 |
| Entity Tax Identification Number | 84-4465489 |
| Entity Address, Address Line One | 6720 Via Austi Parkway, Suite 450 |
| Entity Address, City or Town | Las Vegas |
| Entity Address, State or Province | NV |
| Entity Address, Postal Zip Code | 89119 |
| City Area Code | 702 |
| Local Phone Number | 844-6111 |
| Written Communications | false |
| Soliciting Material | false |
| Pre-commencement Tender Offer | false |
| Pre-commencement Issuer Tender Offer | false |
| Title of 12(b) Security | Common Stock, par value of $0.0001 per share |
| Trading Symbol | MP |
| Security Exchange Name | NYSE |
| Entity Emerging Growth Company | false |
| Entity Central Index Key | 0001801368 |
| Amendment Flag | false |
