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Fair Value of Derivative and Other Financial Instruments - Debt Maturities (Details)	9 Months Ended
	Sep. 30, 2016 USD ($)
Debt Maturities [Line Items]
Held-to-maturity Securities, Continuous Unrealized Loss Position, Fair Value	$ 0
Held-to-Maturity
Other than Temporary Impairment Losses, Investments, Portion in Other Comprehensive Loss, before Tax, Including Portion Attributable to Noncontrolling Interest	0
PNMR and PNM [Member]
Available-for-Sale
Within 1 year	4,349,000
After 1 year through 5 years	36,265,000
After 5 years through 10 years	24,512,000
After 10 years through 15 years	10,286,000
After 15 years through 20 years	9,446,000
After 20 years	41,380,000
Available-for-sale debt securities	126,238,000
PNM Resources [Member]
Held-to-Maturity
Within 1 year	0
After 1 year through 5 years	119,987,000
After 5 years through 10 years	0
Held-to-maturity debt securities	$ 119,987,000

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- Definition

Available-for-sale Securities, Debt Maturities, after Fifteen Years Through Twenty Years, Fair Value

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Available-for-sale Securities, Debt Maturities, after Ten Years Through Fifteen Years, Fair Value

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Fair value of available-for-sale debt securities maturing in the sixth fiscal year through the tenth 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.

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-Publisher FASB
-Name Accounting Standards Codification
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-SubTopic 320
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Fair value of available-for-sale debt securities maturing in the second fiscal year through the fifth 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.

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Amount of debt securities categorized neither as held-to-maturity nor trading.

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Fair value of investments in debt securities classified as held-to-maturity.

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Amount before tax of other than temporary impairment (OTTI) loss on investments in available-for-sale and held-to-maturity debt securities, recognized in other comprehensive loss.

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