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Segment Information - Major Customers (Details) - Electric operating revenues - customer	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
PNMR and PNM
Concentration Risk [Line Items]
Number of customers that make up more than 10% of total revenue	0
PNMR and PNM | Maximum
Concentration Risk [Line Items]
Operating revenues from continuing operations	10.00%
Texas-New Mexico Power Company
Concentration Risk [Line Items]
Number of customers that make up more than 10% of total revenue	3
Texas-New Mexico Power Company | REP A
Concentration Risk [Line Items]
Operating revenues from continuing operations	21.00%	16.00%	16.00%
Texas-New Mexico Power Company | REP B
Concentration Risk [Line Items]
Operating revenues from continuing operations	15.00%	11.00%	11.00%
Texas-New Mexico Power Company | REP C
Concentration Risk [Line Items]
Operating revenues from continuing operations	12.00%	10.00%	11.00%

X

- Definition

Number of Customers that make up 10 percent of total revenue

+ References

No definition available.

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- Definition

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- Definition

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+ References

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