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v3.20.4

Financing - Short-term Debt and Liquidity (Details) | 12 Months Ended |  |  |  |
--- | --- | --- | --- | --- | ---
Dec. 31, 2020 USD ($) numberOfAMIMeters | Feb. 19, 2021 USD ($) | Jun. 30, 2020 USD ($) | Dec. 31, 2019 USD ($) | Jul. 22, 2019 USD ($)
Short-term Debt [Line Items] |  |  |  |  |
Financing capacity | $ 40,000,000.0 |  |  |  | $ 50,000,000.0
Short-term debt | 32,000,000 |  |  | $ 185,100,000 |
Letters of credit outstanding | 4,700,000 |  |  |  |
JPMorgan Chase Bank, N.A. |  |  |  |  |
Short-term Debt [Line Items] |  |  |  |  |
Letters of credit outstanding | 30,300,000 |  |  |  |
PNM Resources |  |  |  |  |
Short-term Debt [Line Items] |  |  |  |  |
Short-term debt | 12,000,000 |  |  | 112,100,000 |
Pollution Control Revenue Bonds | Bonds |  |  |  |  |
Short-term Debt [Line Items] |  |  |  |  |
Aggregate principal amount |  |  | $ 100,300,000 |  |
PNMR Revolving Credit Facility |  |  |  |  |
Short-term Debt [Line Items] |  |  |  |  |
Financing capacity | 300,000,000.0 |  |  |  |
Short-term debt | $ 12,000,000 |  |  | 112,100,000 |
PNMR Revolving Credit Facility | PNM Resources |  |  |  |  |
Short-term Debt [Line Items] |  |  |  |  |
Interest rates on outstanding borrowings | 1.66% |  |  |  |
PNMR Development Revolving Credit Facility |  |  |  |  |
Short-term Debt [Line Items] |  |  |  |  |
Short-term debt | $ 10,000,000 |  |  | 0 |
PNM |  |  |  |  |
Short-term Debt [Line Items] |  |  |  |  |
Short-term debt | 10,000,000 |  |  | 58,000,000 |
Letters of credit outstanding | 2,200,000 |  |  |  |
PNM | Lines of credit |  |  |  |  |
Short-term Debt [Line Items] |  |  |  |  |
NMPRC approved credit facility | 40,000,000.0 |  |  |  |
PNM | PNM Revolving Credit Facility |  |  |  |  |
Short-term Debt [Line Items] |  |  |  |  |
Financing capacity | 400,000,000.0 |  |  |  |
Short-term debt | 0 |  |  | 48,000,000 |
PNM | PNM 2017 New Mexico Credit Facility |  |  |  |  |
Short-term Debt [Line Items] |  |  |  |  |
Short-term debt | $ 10,000,000 |  |  | 10,000,000 |
Interest rates on outstanding borrowings | 1.41% |  |  |  |
TNMP |  |  |  |  |
Short-term Debt [Line Items] |  |  |  |  |
Short-term debt | $ 0 |  |  | 15,000,000 |
Letters of credit outstanding | 0 |  |  |  |
TNMP | TNMP Revolving Credit Facility |  |  |  |  |
Short-term Debt [Line Items] |  |  |  |  |
Financing capacity | 75,000,000.0 |  |  |  |
Short-term debt | $ 0 |  |  | $ 15,000,000 |
Interest rates on outstanding borrowings | 1.15% |  |  |  |
TNMP | TNMP Revolving Credit Facility | First Mortgage Bonds at 9.50% due 2019 |  |  |  |  |
Short-term Debt [Line Items] |  |  |  |  |
Aggregate principal amount of bonds | $ 75,000,000.0 |  |  |  |
PNM and TNMP | PNMR Development Revolving Credit Facility |  |  |  |  |
Short-term Debt [Line Items] |  |  |  |  |
Letters of credit outstanding | $ 0 |  |  |  |
Revolving Credit Facility | TNMP | First Mortgage Bonds at 9.50% due 2019 |  |  |  |  |
Short-term Debt [Line Items] |  |  |  |  |
Number of extension options | numberOfAMIMeters | 2 |  |  |  |
Extension option period | 1 year |  |  |  |
Subsequent Event | PNM Resources |  |  |  |  |
Short-term Debt [Line Items] |  |  |  |  |
Consolidated invested cash |  | $ 900,000 |  |  |
Subsequent Event | PNMR Revolving Credit Facility |  |  |  |  |
Short-term Debt [Line Items] |  |  |  |  |
Available borrowing capacity |  | 257,700,000 |  |  |
Subsequent Event | Revolving Credit Facility |  |  |  |  |
Short-term Debt [Line Items] |  |  |  |  |
Available borrowing capacity |  | 773,100,000 |  |  |
Subsequent Event | PNM |  |  |  |  |
Short-term Debt [Line Items] |  |  |  |  |
Consolidated invested cash |  | 32,600,000 |  |  |
Subsequent Event | PNM | PNM Revolving Credit Facility |  |  |  |  |
Short-term Debt [Line Items] |  |  |  |  |
Available borrowing capacity |  | 397,800,000 |  |  |
Subsequent Event | PNM | PNM 2017 New Mexico Credit Facility |  |  |  |  |
Short-term Debt [Line Items] |  |  |  |  |
Available borrowing capacity |  | 40,000,000.0 |  |  |
Subsequent Event | TNMP |  |  |  |  |
Short-term Debt [Line Items] |  |  |  |  |
Consolidated invested cash |  | 0 |  |  |
Subsequent Event | TNMP | TNMP Revolving Credit Facility |  |  |  |  |
Short-term Debt [Line Items] |  |  |  |  |
Available borrowing capacity |  | 47,600,000 |  |  |
Subsequent Event | PNMR Development | TNMP Revolving Credit Facility |  |  |  |  |
Short-term Debt [Line Items] |  |  |  |  |
Available borrowing capacity |  | $ 30,000,000.0 |  |  |

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