| Cover Page | Dec. 15, 2020 |
| Entity Information [Line Items] | |
| Document Type | 8-K |
| Document Period End Date | Dec. 15, 2020 |
| Entity File Number | 001-32462 |
| Entity Registrant Name | PNM Resources, Inc. |
| Entity Tax Identification Number | 85-0468296 |
| Entity Incorporation, State or Country Code | NM |
| Entity Address, Address Line One | 414 Silver Ave. SW |
| Entity Address, City or Town | Albuquerque |
| Entity Address, State or Province | NM |
| Entity Address, Postal Zip Code | 87102-3289 |
| City Area Code | 505 |
| Local Phone Number | 241-2700 |
| Written Communications | false |
| Soliciting Material | false |
| Pre-commencement Tender Offer | false |
| Pre-commencement Issuer Tender Offer | false |
| Title of 12(b) Security | Common Stock, no par value |
| Trading Symbol | PNM |
| Security Exchange Name | NYSE |
| Entity Emerging Growth Company | false |
| Entity Central Index Key | 0001108426 |
| Amendment Flag | false |
