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Pension and Other Postretirement Benefits - Pre-Tax Information about Prior Service Cost and Net Actuarial (Gain) loss in AOCI (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2018 USD ($)
Public Service Company of New Mexico | Pension Plan
Prior service cost
Amounts in AOCI not yet recognized in net periodic benefit cost (income) at beginning of year	$ (1,045)
Experience (gain) loss	0
Regulatory asset (liability) adjustment	1,045
Amortization recognized in net periodic benefit cost (income)	0
Amounts in AOCI not yet recognized in net periodic benefit cost (income) at end of year	0
Amortization expected to be recognized in 2019	0
Other Comprehensive Income (Loss), Defined Benefit Plan, Gain (Loss), after Reclassification Adjustment, before Tax [Abstract]
Amounts in AOCI not yet recognized in net periodic benefit cost (income) at beginning of year	148,526
Experience (gain) loss	22,728
Regulatory asset (liability) adjustment	(13,571)
Amortization recognized in net periodic benefit cost (income)	(7,409)
Amounts in AOCI not yet recognized in net periodic benefit cost (income) at end of year	150,274
Amortization expected to be recognized in 2019	7,270
Public Service Company of New Mexico | Executive Retirement Program
Other Comprehensive Income (Loss), Defined Benefit Plan, Gain (Loss), after Reclassification Adjustment, before Tax [Abstract]
Amounts in AOCI not yet recognized in net periodic benefit cost (income) at beginning of year	2,450
Experience (gain) loss	(508)
Regulatory asset (liability) adjustment	295
Amortization recognized in net periodic benefit cost (income)	(151)
Amounts in AOCI not yet recognized in net periodic benefit cost (income) at end of year	2,086
Amortization expected to be recognized in 2019	133
Texas-New Mexico Power Company | Pension Plan
Other Comprehensive Income (Loss), Defined Benefit Plan, Gain (Loss), after Reclassification Adjustment, before Tax [Abstract]
Amounts in AOCI not yet recognized in net periodic benefit cost (income) at beginning of year	0
Experience (gain) loss	1,926
Regulatory asset (liability) adjustment	(1,926)
Amortization recognized in net periodic benefit cost (income)	0
Amounts in AOCI not yet recognized in net periodic benefit cost (income) at end of year	0
Amortization expected to be recognized in 2019	0
Texas-New Mexico Power Company | Executive Retirement Program
Other Comprehensive Income (Loss), Defined Benefit Plan, Gain (Loss), after Reclassification Adjustment, before Tax [Abstract]
Amounts in AOCI not yet recognized in net periodic benefit cost (income) at beginning of year	0
Experience (gain) loss	4
Regulatory asset (liability) adjustment	(4)
Amortization recognized in net periodic benefit cost (income)	0
Amounts in AOCI not yet recognized in net periodic benefit cost (income) at end of year	0
Amortization expected to be recognized in 2019	$ 0

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Amount, before tax, of accumulated other comprehensive (income) loss for cost (credit) of benefit change attributable to participants' prior service from plan amendment or plan initiation of defined benefit plan, that has not been recognized in net periodic benefit cost (credit).

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Amount included in accumulated other comprehensive income (loss) for gain (loss) of defined benefit plan expected to be recognized in net periodic benefit (cost) credit for fiscal year following most recent annual statement of financial position.

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Amount, before tax, of cost (credit) of benefit change attributable to participants' prior service from plan amendment or plan initiation of defined benefit plan, that has not been recognized in net periodic benefit cost (credit).

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