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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, 2019 USD ($)
Public Service Company of New Mexico | Pension Plan
Net actuarial (gain) loss
Amounts in AOCI not yet recognized in net periodic benefit cost (income) at beginning of year	$ 150,274
Experience (gain) loss	8,926
Regulatory asset (liability) adjustment	(5,539)
Amortization recognized in net periodic benefit cost (income)	(7,270)
Amounts in AOCI not yet recognized in net periodic benefit cost (income) at end of year	146,391
Amortization expected to be recognized in 2020	8,131
Public Service Company of New Mexico | Executive Retirement Program
Net actuarial (gain) loss
Amounts in AOCI not yet recognized in net periodic benefit cost (income) at beginning of year	2,086
Experience (gain) loss	1,053
Regulatory asset (liability) adjustment	(611)
Amortization recognized in net periodic benefit cost (income)	(133)
Amounts in AOCI not yet recognized in net periodic benefit cost (income) at end of year	2,395
Amortization expected to be recognized in 2020	169
Texas-New Mexico Power Company | Pension Plan
Net actuarial (gain) loss
Amounts in AOCI not yet recognized in net periodic benefit cost (income) at beginning of year	0
Experience (gain) loss	1,877
Regulatory asset (liability) adjustment	(1,877)
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 2020	0
Texas-New Mexico Power Company | Executive Retirement Program
Net actuarial (gain) loss
Amounts in AOCI not yet recognized in net periodic benefit cost (income) at beginning of year	0
Experience (gain) loss	54
Regulatory asset (liability) adjustment	(54)
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 2020	$ 0

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