Debt Instruments, NMPRC Approved credit facility

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- Definition

Lease term extension period

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Number Of Extensions

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Short Term Debt Due to Related Party

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- Definition

Amount of assets pledged to secure a debt instrument.

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- Definition

Face (par) amount of debt instrument at time of issuance.

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- Definition

Contractual interest rate for funds borrowed, under the debt agreement.

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- Definition

Period of time between issuance and maturity of debt instrument, in PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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No definition available.

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- Definition

Fixed interest rate related to the interest rate derivative.

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No definition available.

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- Definition

The number of derivative instruments of a particular group held by the entity.

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- Definition

The total amount of the contingent obligation under letters of credit outstanding as of the reporting date.

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No definition available.

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- Definition

Maximum borrowing capacity under the credit facility without consideration of any current restrictions on the amount that could be borrowed or the amounts currently outstanding under the facility.

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Amount of borrowing capacity currently available under the credit facility (current borrowing capacity less the amount of borrowings outstanding).

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Maximum period the entity is hedging its exposure to the variability in future cash flows for forecasted transactions, excluding those forecasted transactions related to the payment of variable interest on existing financial instruments, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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Amount of long-term debt classified as other.

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- Definition

Cash and investments whose use in whole or in part is restricted for the long-term, generally by contractual agreements or regulatory requirements. For use in an unclassified balance sheet.

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- Definition

Reflects the total carrying amount as of the balance sheet date of debt having initial terms less than one year or the normal operating cycle, if longer.

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Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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Weighted average interest rate of short-term debt outstanding calculated at point in time.

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Amount of unrealized gain (loss) related to the increase or decrease in fair value of interest rate derivatives designated as cash flow hedging instruments, which was recorded in accumulated other comprehensive income to the extent that the cash flow hedge was determined to be effective.

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Financing - Short-term Debt and Liquidity (Details)	1 Months Ended	6 Months Ended	12 Months Ended
Financing - Short-term Debt and Liquidity (Details)	Jul. 31, 2018 USD ($) Extension	Jun. 30, 2018 USD ($)	Dec. 31, 2017 USD ($) derivative	Nov. 01, 2020 USD ($)	Jul. 25, 2018 USD ($)	Jul. 24, 2018 USD ($)	Jun. 28, 2018 USD ($)	Mar. 09, 2018 USD ($)	Feb. 26, 2018 USD ($)	Jul. 28, 2017 USD ($)	Jul. 20, 2017 USD ($)	Dec. 21, 2016 USD ($)
Short-term Debt [Line Items]
Short-term debt		$ 282,600,000	$ 305,400,000
Letters of credit outstanding		6,500,000
Other Long-term Debt		0
Senior Unsecured Notes
Short-term Debt [Line Items]
Debt issued								$ 300,000,000.0
Stated interest rate								3.25%
Subsequent event
Short-term Debt [Line Items]
Remaining borrowing capacity					$ 669,900,000
PNMR \| Subsequent event
Short-term Debt [Line Items]
Short-term debt – affiliate						$ 0
Remaining borrowing capacity					182,500,000
Consolidated invested cash					900,000
PNMR Development Revolving Credit Facility
Short-term Debt [Line Items]
Short-term debt		24,500,000	0
PNMR 2016 One-Year Term Loan (as extended)
Short-term Debt [Line Items]
Short-term debt		$ 100,000,000	$ 100,000,000									$ 100,000,000.0
Weighted-average interest rate for short-term debt		2.89%
Term of loan		1 year
PNMR 2016 One-Year Term Loan (as extended) \| Subsequent event
Short-term Debt [Line Items]
Term of loan	1 year
Variable Rate Short-Term Debt
Short-term Debt [Line Items]
Term of derivatives			4 years
Debt issued			$ 50,000,000.0
PNMR 2016 Two-Year Term Loan
Short-term Debt [Line Items]
Short-term debt												$ 100,000,000.0
Term of loan		2 years
PNMR 2016 Two-Year Term Loan \| Subsequent event
Short-term Debt [Line Items]
Term of loan	2 years
PNMR Revolving Credit Facility
Short-term Debt [Line Items]
Financing capacity		$ 10,000,000.0
PNMR Revolving Credit Facility \| Subsequent event
Short-term Debt [Line Items]
Number Of Extensions \| Extension	2
Lease term extension period	1 year
PNMR Revolving Credit Facility \| PNMR
Short-term Debt [Line Items]
Weighted-average interest rate for short-term debt		3.33%
PNMR Revolving Credit Facility \| Forecast
Short-term Debt [Line Items]
Financing capacity				$ 290,000,000.0
PNM Revolving Credit Facility \| PNMR
Short-term Debt [Line Items]
Weighted-average interest rate for short-term debt		3.22%
PNM 2017 New Mexico Credit Facility \| PNMR
Short-term Debt [Line Items]
Weighted-average interest rate for short-term debt		3.22%
TNMP Revolving Credit Facility \| PNMR
Short-term Debt [Line Items]
Weighted-average interest rate for short-term debt		2.84%
PNMR Development Revolving Credit Facility \| PNMR
Short-term Debt [Line Items]
Weighted-average interest rate for short-term debt		3.05%
PNM
Short-term Debt [Line Items]
Short-term debt		$ 33,600,000	39,800,000
Letters of credit outstanding		2,500,000
Short-term debt – affiliate		4,900,000	0
PNM \| Subsequent event
Short-term Debt [Line Items]
Remaining borrowing capacity					388,700,000
Consolidated invested cash					0
PNM \| Lines of credit
Short-term Debt [Line Items]
NMPRC approved credit facility		40,000,000
Short-term debt		$ 10,000,000	0
PNM \| Lines of credit \| Subsequent event
Short-term Debt [Line Items]
Remaining borrowing capacity					30,000,000
PNM \| Senior Unsecured Notes, Due 2018, at 7 point 50 percent \| Unsecured debt
Short-term Debt [Line Items]
Stated interest rate		7.50%								7.50%
PNM \| Forecast \| SUNs, Issuance in August 2018 \| Senior Unsecured Notes
Short-term Debt [Line Items]
Debt issued	$ 100,000,000.0
PNM \| Plan \| SUNs, Issuance in August 2018 \| Senior Unsecured Notes
Short-term Debt [Line Items]
Debt issued		$ 100,000,000								$ 100,000,000.0
PNM \| PNM Revolving Credit Facility
Short-term Debt [Line Items]
Financing capacity		40,000,000.0
PNM \| PNM Revolving Credit Facility \| Forecast
Short-term Debt [Line Items]
Financing capacity				$ 360,000,000.0
TNMP
Short-term Debt [Line Items]
Short-term debt		13,500,000	0
Letters of credit outstanding		100,000
Short-term debt – affiliate		100,000	0
TNMP \| Subsequent event
Short-term Debt [Line Items]
Remaining borrowing capacity					68,700,000
Consolidated invested cash					$ 0
TNMP \| First Mortgage Bonds \| Mortgages
Short-term Debt [Line Items]
Debt issued		172,300,000.0					$ 60,000,000.0
Stated interest rate							3.85%
TNMP \| First Mortgage Bonds \| Subsequent event \| Mortgages
Short-term Debt [Line Items]
Stated interest rate					2.76%
PNMR Development \| Subsequent event
Short-term Debt [Line Items]
Remaining borrowing capacity					$ 0
PNMR Development \| PNMR 2018 Revolving Credit Facility
Short-term Debt [Line Items]
Financing capacity									$ 24,500,000.0
Revolving credit facility
Short-term Debt [Line Items]
Financing capacity		300,000,000.0
Short-term debt		111,000,000	165,600,000
Revolving credit facility \| PNM
Short-term Debt [Line Items]
Financing capacity		400,000,000.0
Short-term debt		23,600,000	39,800,000
Revolving credit facility \| TNMP
Short-term Debt [Line Items]
Financing capacity		75,000,000.0
Short-term debt		13,500,000	$ 0
Revolving credit facility \| TNMP \| First mortgage bonds
Short-term Debt [Line Items]
Collateral amount		75,000,000
Affiliated entity \| PNM \| Subsequent event
Short-term Debt [Line Items]
Short-term debt – affiliate					20,000,000
Affiliated entity \| TNMP \| Subsequent event
Short-term Debt [Line Items]
Short-term debt – affiliate					$ 3,500,000.0
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]
Fair value gain (loss)		$ 3,700,000	$ 1,400,000
JPMorgan Chase Bank, N.A. and U.S. Bank National Association \| PNM \| PNM 2017 Term Loan Agreement \| Term loan agreement with banks
Short-term Debt [Line Items]
Debt issued											$ 200,000,000.0