Debt Instruments, NMPRC Approved credit facility

No definition available.

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Namespace Prefix:	pnm_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Short Term Debt Due to Related Party

+ References

No definition available.

+ Details

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Namespace Prefix:	pnm_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Amount of assets pledged to secure a debt instrument.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 470
-Section 50
-Paragraph 3
-Subparagraph (d)
-URI http://asc.fasb.org/extlink&oid=75038535&loc=d3e64711-112823

+ Details

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Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

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

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 835
-SubTopic 30
-Section 55
-Paragraph 8
-URI http://asc.fasb.org/extlink&oid=64930739&loc=d3e28878-108400

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 835
-SubTopic 30
-Section 45
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=64930785&loc=d3e28551-108399

+ Details

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Data Type:	xbrli:monetaryItemType
Balance Type:	credit
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.

+ Details

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Data Type:	xbrli:durationItemType
Balance Type:	na
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

Name:	us-gaap_LettersOfCreditOutstandingAmount
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- 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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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

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

+ References

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Amount of long-term debt payable, sinking fund requirements, and other securities issued that are redeemable by holder at fixed or determinable prices and dates maturing in the next rolling twelve months following the latest balance sheet. For interim and annual periods when interim periods are reported on a rolling approach, from latest balance sheet date.

+ References

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Amount of long-term debt payable, sinking fund requirements, and other securities issued that are redeemable by holder at fixed or determinable prices and dates maturing in the next fiscal year following the latest fiscal year. Excludes interim and annual periods when interim periods are reported on a rolling approach, from latest balance sheet date.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 235
-SubTopic 10
-Section S99
-Paragraph 3
-Subparagraph (SX 210.12-04.(a))
-URI http://asc.fasb.org/extlink&oid=26873400&loc=d3e24072-122690

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 470
-SubTopic 10
-Section 50
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=6802200&loc=d3e1835-112601

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Amount of long-term debt payable, sinking fund requirements, and other securities issued that are redeemable by holder at fixed or determinable prices and dates maturing in the second rolling twelve months following the latest balance sheet. For interim and annual periods when interim periods are reported on a rolling approach, from latest balance sheet date.

+ References

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Amount of long-term debt payable, sinking fund requirements, and other securities issued that are redeemable by holder at fixed or determinable prices and dates maturing in the second fiscal year following the latest fiscal year. Excludes interim and annual periods when interim periods are reported on a rolling approach, from latest balance sheet date.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 470
-SubTopic 10
-Section 50
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=6802200&loc=d3e1835-112601

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 235
-SubTopic 10
-Section S99
-Paragraph 3
-Subparagraph (SX 210.12-04.(a))
-URI http://asc.fasb.org/extlink&oid=26873400&loc=d3e24072-122690

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Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

The amount for notes payable (written promise to pay), due to related parties. Used to reflect the current portion of the liabilities (due within one year or within the normal operating cycle if longer).

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 235
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.4-08.(k)(1))
-URI http://asc.fasb.org/extlink&oid=26873400&loc=d3e23780-122690

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 850
-SubTopic 10
-Section 50
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=6457730&loc=d3e39549-107864

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.19(a)(5))
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- 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.

+ Details

Name:	us-gaap_RestrictedCashAndInvestments
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- 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.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02(19)(a))
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-03(13))
-URI http://asc.fasb.org/extlink&oid=6876686&loc=d3e534808-122878

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.7-03(a)(16)(a)(1))
-URI http://asc.fasb.org/extlink&oid=6879938&loc=d3e572229-122910

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
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

Name:	us-gaap_ShortTermDebtLineItems
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Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

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

+ References

+ Details

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Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

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- Details

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Name:	us-gaap_DebtInstrumentAxis=pnm_LocalLinesOfCreditMember
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- Details

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- Details

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Financing - Short-term Debt and Liquidity (Details) - USD ($)	6 Months Ended
	Jun. 30, 2017	Nov. 01, 2020	Jul. 28, 2017	Jul. 25, 2017	Dec. 31, 2016	Nov. 30, 2016
Short-term Debt [Line Items]
Short-term debt	$ 373,500,000				$ 287,100,000
Letters of credit outstanding	6,400,000
Maturities and other repayments due in next 12 months	274,800,000
Maturities and other repayments due in the remainder of year two	$ 104,600,000
Subsequent event
Short-term Debt [Line Items]
Remaining borrowing capacity				$ 581,300,000
PNMR \| Subsequent event
Short-term Debt [Line Items]
Remaining borrowing capacity				119,900,000
Consolidated invested cash				1,500,000
PNMR 2016 One-Year Term Loan
Short-term Debt [Line Items]
Weighted-average interest rate for short-term debt	2.07%
Term of loan	1 year
Short-term debt	$ 100,000,000				100,000,000
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	2.43%
PNMR Revolving Credit Facility \| Forecast
Short-term Debt [Line Items]
Financing capacity		$ 290,000,000.0
PNM
Short-term Debt [Line Items]
Short-term debt	$ 38,000,000				61,000,000
Letters of credit outstanding	2,500,000
PNM \| PNM 2016 Term Loan Agreement
Short-term Debt [Line Items]
Debt issued	175,000,000.0
PNM \| Subsequent event
Short-term Debt [Line Items]
Remaining borrowing capacity				388,500,000
Consolidated invested cash				0
PNM \| Lines of credit
Short-term Debt [Line Items]
NMPRC approved credit facility	50,000,000
Short-term debt	10,000,000				26,000,000
Maturities and other repayments due	$ 50,000,000
PNM \| Lines of credit \| Subsequent event
Short-term Debt [Line Items]
Remaining borrowing capacity				50,000,000
PNM \| Senior Unsecured Note Agreement (SUNs) \| Subsequent event \| Senior Unsecured Notes
Short-term Debt [Line Items]
Debt issued			$ 450,000,000.0
PNM \| PNM Revolving Credit Facility
Short-term Debt [Line Items]
Financing capacity						$ 40,000,000.0
Weighted-average interest rate for short-term debt	2.33%
PNM \| PNM Revolving Credit Facility \| Forecast
Short-term Debt [Line Items]
Financing capacity		$ 360,000,000.0
PNM \| PNM New Mexico Credit Facility
Short-term Debt [Line Items]
Weighted-average interest rate for short-term debt	2.36%
TNMP
Short-term Debt [Line Items]
Short-term debt	$ 47,000,000				0
Letters of credit outstanding	100,000
Intercompany borrowings	8,000,000
Short-term debt – affiliate	8,000,000				4,600,000
Maturities and other repayments due	$ 0
TNMP \| Subsequent event
Short-term Debt [Line Items]
Remaining borrowing capacity				22,900,000
Consolidated invested cash				0
TNMP \| Subsequent event \| Affiliated entity
Short-term Debt [Line Items]
Short-term debt – affiliate				$ 1,400,000
TNMP \| PNM Revolving Credit Facility
Short-term Debt [Line Items]
Weighted-average interest rate for short-term debt	2.13%
Revolving credit facility
Short-term Debt [Line Items]
Financing capacity	$ 300,000,000.0
Short-term debt	188,500,000				126,100,000
Revolving credit facility \| PNM
Short-term Debt [Line Items]
Financing capacity	400,000,000.0
Short-term debt	28,000,000				35,000,000
Revolving credit facility \| TNMP
Short-term Debt [Line Items]
Financing capacity	75,000,000.0
Short-term debt	47,000,000				$ 0
Maturities and other repayments due in 2018	75,000,000
Revolving credit facility \| TNMP \| First mortgage bonds
Short-term Debt [Line Items]
Collateral amount	$ 75,000,000