Debt Instruments, NMPRC Approved credit facility

No definition available.

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- Definition

Short Term Debt Due to Related Party

+ References

No definition available.

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- Definition

Amount of assets pledged to secure a debt instrument.

+ References

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-Publisher FASB
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- Definition

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

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Period Type:	instant

- Definition

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

+ References

+ Details

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Period Type:	instant

- 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.

+ References

No definition available.

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Period Type:	duration

- Definition

Fixed interest rate related to the interest rate derivative.

+ References

No definition available.

+ Details

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Balance Type:	na
Period Type:	instant

- Definition

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

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- Definition

Gross amount of debt extinguished.

+ References

No definition available.

+ Details

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Balance Type:	debit
Period Type:	duration

- Definition

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

+ References

No definition available.

+ Details

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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.

+ References

+ Details

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Period Type:	instant

- Definition

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

+ References

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- Definition

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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- Definition

Amount, before tax, of reclassification of gain (loss) from accumulated other comprehensive income (AOCI) for derivative instrument designated and qualifying as cash flow hedge included in assessment of hedge effectiveness.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
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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.

+ References

No definition available.

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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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Period Type:	instant

- Definition

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.

+ References

No definition available.

+ Details

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- Definition

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

+ References

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- Definition

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)			3 Months Ended	12 Months Ended
Financing - Short-term Debt and Liquidity (Details)	Apr. 01, 2019 USD ($)	Jan. 18, 2019 USD ($)	Mar. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)	Dec. 31, 2017 USD ($) derivative	Jul. 01, 2019 USD ($)	May 03, 2019 USD ($)	Mar. 29, 2019 USD ($)	Feb. 26, 2019 USD ($)	Feb. 22, 2019 USD ($)	Feb. 21, 2019 USD ($)
Short-term Debt [Line Items]
Financing capacity										$ 25,000,000.0	$ 24,500,000.0
Short-term debt			$ 223,800,000	$ 235,900,000
Letters of credit outstanding			4,700,000
Subsequent event
Short-term Debt [Line Items]
Remaining borrowing capacity							$ 732,500,000
PNMR \| Subsequent event
Short-term Debt [Line Items]
Remaining borrowing capacity							239,400,000
Consolidated invested cash							900,000
PNMR 2018 One-Year Term Loan
Short-term Debt [Line Items]
Short-term debt			$ 150,000,000	150,000,000
Term of loan			1 year
PNMR 2018 One-Year Term Loan \| PNMR
Short-term Debt [Line Items]
Weighted-average interest rate for short-term debt			3.24%
PNMR Development Revolving Credit Facility
Short-term Debt [Line Items]
Short-term debt			$ 11,600,000	6,000,000
Variable Rate Short-Term Debt
Short-term Debt [Line Items]
Term of derivatives					4 years
Debt issued					$ 50,000,000.0
PNMR Revolving Credit Facility
Short-term Debt [Line Items]
Financing capacity			$ 10,000,000.0
PNMR Revolving Credit Facility \| PNMR
Short-term Debt [Line Items]
Weighted-average interest rate for short-term debt			3.74%
PNMR Development Revolving Credit Facility \| PNMR
Short-term Debt [Line Items]
Weighted-average interest rate for short-term debt			3.49%
PNM
Short-term Debt [Line Items]
Short-term debt			$ 0	42,400,000
Letters of credit outstanding			2,500,000
Short-term debt – affiliate			0	19,800,000
PNM \| Subsequent event
Short-term Debt [Line Items]
Remaining borrowing capacity							397,500,000
Consolidated invested cash							9,000,000
PNM \| Lines of credit
Short-term Debt [Line Items]
NMPRC approved credit facility			40,000,000
Short-term debt			0	10,000,000
PNM \| Lines of credit \| Subsequent event
Short-term Debt [Line Items]
Remaining borrowing capacity							40,000,000
PNM \| PNM Revolving Credit Facility
Short-term Debt [Line Items]
Financing capacity			40,000,000.0
TNMP
Short-term Debt [Line Items]
Short-term debt			0	17,500,000
Letters of credit outstanding			700,000
Short-term debt – affiliate			0	100,000
TNMP \| Subsequent event
Short-term Debt [Line Items]
Remaining borrowing capacity							45,700,000
Consolidated invested cash							0
TNMP \| TNMP 2019 Bond Purchase Agreement
Short-term Debt [Line Items]
Debt issued								$ 225,000,000	$ 305,000,000.0
TNMP \| First mortgage bonds
Short-term Debt [Line Items]
Extinguishment of debt		$ 172,300,000
Stated interest rate		9.50%
TNMP \| PNMR 2018 One-Year Term Loan
Short-term Debt [Line Items]
Debt issued								150,000,000
TNMP \| First Mortgage Bonds 3.60 Percent Due 2029 \| Subsequent event
Short-term Debt [Line Items]
Debt issued						$ 80,000,000
PNMR Development
Short-term Debt [Line Items]
Short-term debt – affiliate			3,100,000	0
PNMR Development \| Subsequent event
Short-term Debt [Line Items]
Remaining borrowing capacity							$ 9,900,000
Revolving credit facility
Short-term Debt [Line Items]
Financing capacity			300,000,000.0
Short-term debt			62,200,000	20,000,000
Revolving credit facility \| PNM
Short-term Debt [Line Items]
Financing capacity			400,000,000.0
Short-term debt			0	32,400,000
Revolving credit facility \| TNMP
Short-term Debt [Line Items]
Financing capacity			75,000,000.0
Short-term debt			0	17,500,000
Revolving credit facility \| TNMP \| First mortgage bonds
Short-term Debt [Line Items]
Collateral amount			75,000,000
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)			1,400,000
Fair value gain (loss)				$ 1,000,000
Mortgages \| TNMP \| TNMP 2019 Bond Purchase Agreement
Short-term Debt [Line Items]
Debt issued			$ 305,000,000					$ 225,000,000	$ 305,000,000.0
Stated interest rate									400.00%
Mortgages \| TNMP \| First Mortgage Bonds 3.60 Percent Due 2029 \| Subsequent event
Short-term Debt [Line Items]
Debt issued						$ 80,000,000
Stated interest rate						3.60%
Unsecured Debt \| TNMP \| First mortgage bonds
Short-term Debt [Line Items]
Extinguishment of debt	$ 172,300,000
Stated interest rate	9.50%