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v3.20.2

Financing - Short-term Debt and Liquidity (Details) |  | 9 Months Ended | 12 Months Ended |  |  |  |
--- | --- | --- | --- | --- | --- | --- | ---
Oct. 20, 2020 USD ($) | Sep. 30, 2020 USD ($) numberOfAMIMeters | Dec. 31, 2017 USD ($) derivative | Oct. 27, 2020 USD ($) | Dec. 31, 2019 USD ($) | Jul. 22, 2019 USD ($) | Jul. 21, 2019 USD ($)
Short-term Debt [Line Items] |  |  |  |  |  |  |
Financing capacity |  |  |  |  |  | $ 50,000,000.0 | $ 40,000,000.0
Short-term debt |  | $ 184,294,000 |  |  | $ 185,100,000 |  |
Letters of credit outstanding |  | 4,700,000 |  |  |  |  |
Bonds |  |  |  |  |  |  |
Short-term Debt [Line Items] |  |  |  |  |  |  |
Aggregate principal amount |  | 302,500,000 |  |  |  |  |
Senior Unsecured Notes |  |  |  |  |  |  |
Short-term Debt [Line Items] |  |  |  |  |  |  |
Aggregate principal amount |  | $ 300,000,000.0 |  |  |  |  |
Variable Rate Short-Term Debt |  |  |  |  |  |  |
Short-term Debt [Line Items] |  |  |  |  |  |  |
Term of derivatives |  |  | 4 years |  |  |  |
Aggregate principal amount |  |  | $ 50,000,000.0 |  |  |  |
Pollution Control Revenue Bonds | Bonds |  |  |  |  |  |  |
Short-term Debt [Line Items] |  |  |  |  |  |  |
Stated interest rate |  | 0.32% |  |  |  |  |
PNMR Development Term Loan |  |  |  |  |  |  |
Short-term Debt [Line Items] |  |  |  |  |  |  |
Aggregate principal amount |  | $ 90,000,000.0 |  |  |  |  |
PNMR 2018 Two Year Term Loan |  |  |  |  |  |  |
Short-term Debt [Line Items] |  |  |  |  |  |  |
Aggregate principal amount |  | $ 50,000,000.0 |  |  |  |  |
Term of loan |  | 2 years |  |  |  |  |
PNMR Revolving Credit Facility | PNMR |  |  |  |  |  |  |
Short-term Debt [Line Items] |  |  |  |  |  |  |
Line of credit facility, interest rate at period end |  | 1.66% |  |  |  |  |
PNM |  |  |  |  |  |  |
Short-term Debt [Line Items] |  |  |  |  |  |  |
Short-term debt |  | $ 21,700,000 |  |  | 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 |  |  |  |  |
Short-term debt |  | 20,000,000 |  |  | 10,000,000 |  |
PNM | PNM 2019 Term Loan | Term loan agreement with banks |  |  |  |  |  |  |
Short-term Debt [Line Items] |  |  |  |  |  |  |
Aggregate principal amount |  | 150,000,000.0 |  |  |  |  |
PNM | PNM 2019 40 Million Term Loan |  |  |  |  |  |  |
Short-term Debt [Line Items] |  |  |  |  |  |  |
Aggregate principal amount |  | 40,000,000.0 |  |  |  |  |
PNM | PNM 2020 250 Million Term Loan | Term loan agreement with banks |  |  |  |  |  |  |
Short-term Debt [Line Items] |  |  |  |  |  |  |
Aggregate principal amount |  | 150,000,000.0 |  |  |  |  |
PNM | 5.35% Senior Unsecured Notes due October 2021 |  |  |  |  |  |  |
Short-term Debt [Line Items] |  |  |  |  |  |  |
Aggregate principal amount |  | $ 160,000,000.0 |  |  |  |  |
Stated interest rate |  | 5.35% |  |  |  |  |
PNM | Pollution Control Revenue Bonds at 1.875% | Bonds |  |  |  |  |  |  |
Short-term Debt [Line Items] |  |  |  |  |  |  |
Aggregate principal amount |  | $ 146,000,000.0 |  |  |  |  |
Stated interest rate |  | 1.875% |  |  |  |  |
PNM | PNM Revolving Credit Facility |  |  |  |  |  |  |
Short-term Debt [Line Items] |  |  |  |  |  |  |
Line of credit facility, interest rate at period end |  | 1.40% |  |  |  |  |
PNM | PNM 2017 New Mexico Credit Facility |  |  |  |  |  |  |
Short-term Debt [Line Items] |  |  |  |  |  |  |
Line of credit facility, interest rate at period end |  | 1.41% |  |  |  |  |
PNM | PNMR Development Revolving Credit Facility |  |  |  |  |  |  |
Short-term Debt [Line Items] |  |  |  |  |  |  |
Letters of credit outstanding |  | $ 0 |  |  |  |  |
TNMP |  |  |  |  |  |  |
Short-term Debt [Line Items] |  |  |  |  |  |  |
Short-term debt |  | 494,000 |  |  | 15,000,000 |  |
Letters of credit outstanding |  | 100,000 |  |  |  |  |
TNMP | PNMR Development Term Loan | Term loan agreement with banks |  |  |  |  |  |  |
Short-term Debt [Line Items] |  |  |  |  |  |  |
Aggregate principal amount |  | 90,000,000.0 |  |  |  |  |
Revolving credit facility |  |  |  |  |  |  |
Short-term Debt [Line Items] |  |  |  |  |  |  |
Financing capacity |  | 300,000,000.0 |  |  |  |  |
Short-term debt |  | 162,100,000 |  |  | 112,100,000 |  |
Revolving credit facility | PNM |  |  |  |  |  |  |
Short-term Debt [Line Items] |  |  |  |  |  |  |
Financing capacity |  | 400,000,000.0 |  |  |  |  |
Short-term debt |  | 1,700,000 |  |  | 48,000,000 |  |
Revolving credit facility | TNMP |  |  |  |  |  |  |
Short-term Debt [Line Items] |  |  |  |  |  |  |
Financing capacity |  | 75,000,000.0 |  |  |  |  |
Short-term debt |  | 0 |  |  | 15,000,000 |  |
Revolving credit facility | TNMP | First mortgage bonds |  |  |  |  |  |  |
Short-term Debt [Line Items] |  |  |  |  |  |  |
Collateral amount |  | $ 75,000,000.0 |  |  |  |  |
Number of extension options | numberOfAMIMeters |  | 2 |  |  |  |  |
Extension option period |  | 1 year |  |  |  |  |
Bonds | TNMP |  |  |  |  |  |  |
Short-term Debt [Line Items] |  |  |  |  |  |  |
Short-term debt |  | $ 494,000 |  |  | 0 |  |
Interest rate contract |  |  |  |  |  |  |
Short-term Debt [Line Items] |  |  |  |  |  |  |
Number of derivatives | derivative |  |  | 3 |  |  |  |
Interest rate 1 | Variable Rate Short-Term Debt |  |  |  |  |  |  |
Short-term Debt [Line Items] |  |  |  |  |  |  |
Fixed interest rate |  |  | 1.926% |  |  |  |
Interest rate 2 | Variable Rate Short-Term Debt |  |  |  |  |  |  |
Short-term Debt [Line Items] |  |  |  |  |  |  |
Fixed interest rate |  |  | 1.823% |  |  |  |
Interest rate 3 | Variable Rate Short-Term Debt |  |  |  |  |  |  |
Short-term Debt [Line Items] |  |  |  |  |  |  |
Fixed interest rate |  |  | 1.629% |  |  |  |
Interest rate 3 | Level 2 | Cash Flow Hedge |  |  |  |  |  |  |
Short-term Debt [Line Items] |  |  |  |  |  |  |
Current derivative liability |  | $ 1,500,000 |  |  | $ 400,000 |  |
Subsequent event |  |  |  |  |  |  |
Short-term Debt [Line Items] |  |  |  |  |  |  |
Remaining borrowing capacity |  |  |  | $ 722,400,000 |  |  |
Subsequent event | PNMR |  |  |  |  |  |  |
Short-term Debt [Line Items] |  |  |  |  |  |  |
Remaining borrowing capacity |  |  |  | 129,700,000 |  |  |
Consolidated invested cash |  |  |  | 900,000 |  |  |
Subsequent event | Pollution Control Revenue Bonds | Bonds |  |  |  |  |  |  |
Short-term Debt [Line Items] |  |  |  |  |  |  |
Aggregate principal amount |  |  |  | 100,300,000 |  |  |
Subsequent event | PNM |  |  |  |  |  |  |
Short-term Debt [Line Items] |  |  |  |  |  |  |
Remaining borrowing capacity |  |  |  | 397,800,000 |  |  |
Consolidated invested cash |  |  |  | 13,800,000 |  |  |
Subsequent event | PNM | Lines of credit |  |  |  |  |  |  |
Short-term Debt [Line Items] |  |  |  |  |  |  |
Remaining borrowing capacity |  |  |  | 30,000,000.0 |  |  |
Subsequent event | TNMP |  |  |  |  |  |  |
Short-term Debt [Line Items] |  |  |  |  |  |  |
Remaining borrowing capacity |  |  |  | 74,900,000 |  |  |
Consolidated invested cash |  |  |  | 22,800,000 |  |  |
Subsequent event | PNMR Development |  |  |  |  |  |  |
Short-term Debt [Line Items] |  |  |  |  |  |  |
Remaining borrowing capacity |  |  |  | $ 40,000,000.0 |  |  |
Subsequent event | Term Loan | PNMR | Merger Backstop Facilities |  |  |  |  |  |  |
Short-term Debt [Line Items] |  |  |  |  |  |  |
Financing capacity | $ 50,000,000.0 |  |  |  |  |  |
Remaining borrowing capacity | $ 50,000,000.0 |  |  |  |  |  |
Term of loan | 364 days |  |  |  |  |  |

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