| Cover | Mar. 22, 2022 |
| Cover [Abstract] | |
| Document Type | 8-K |
| Amendment Flag | false |
| Document Period End Date | Mar. 22, 2022 |
| Entity File Number | 001-39644 |
| Entity Registrant Name | ARCHAEA ENERGY INC. |
| Entity Central Index Key | 0001823766 |
| Entity Tax Identification Number | 85-2867266 |
| Entity Incorporation, State or Country Code | DE |
| Entity Address, Address Line One | 4444 Westheimer Road |
| Entity Address, Address Line Two | Suite G450 |
| Entity Address, City or Town | Houston |
| Entity Address, State or Province | TX |
| Entity Address, Postal Zip Code | 77027 |
| City Area Code | 346 |
| Local Phone Number | 708-8272 |
| Written Communications | false |
| Soliciting Material | false |
| Pre-commencement Tender Offer | false |
| Pre-commencement Issuer Tender Offer | false |
| Title of 12(b) Security | Class A common stock, par value $0.0001 per share |
| Trading Symbol | LFG |
| Security Exchange Name | NYSE |
| Entity Emerging Growth Company | true |
| Elected Not To Use the Extended Transition Period | false |
