Pension and Other Postretirement Benefits - Narrative (Details) - USD ($)	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Expected return on plan assets	4.00%
Amortization of gains and losses that are outside the corridor	5 years
Maximum annual contributions per employee	75.00%
Employer matching contribution, percent of employees' gross pay	6.00%
Minimum [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Non-matching contribution of eligible compensation based on eligible employee's age	3.00%
Maximum [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Non-matching contribution of eligible compensation based on eligible employee's age	10.00%
Pension Plan [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Expected long-term return resulting from effect of 1% change	1.00%
Expected long-term return resulting from effect of one-percentage point increase (as a percent)	1.00%
Expected employer contributions to pension plans	$ 0
Pension Plan [Member] | Minimum [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Weighted average discount rate related to anticipated contributions	4.10%
Pension Plan [Member] | Maximum [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Weighted average discount rate related to anticipated contributions	4.90%
Pension Plan [Member] | Equity Securities [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Target plan asset allocations	21.00%
Pension Plan [Member] | Equity Securities [Member] | Developed Countries Outside of United States [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Target plan asset allocations	6.00%
Pension Plan [Member] | Fixed income [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Target plan asset allocations	65.00%
Pension Plan [Member] | Alternative Investments [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Target plan asset allocations	14.00%
Pension Plan [Member] | Public Service Company of New Mexico [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Expected return on plan assets	6.50%	6.80%	7.20%
Expected long-term return on assets decrease resulting in increase net periodic costs In next fiscal year	$ 5,300,000
Actual rate of return for pension plans	5.90%
Actuarial gains (losses) recorded as regulatory assets	$ (43,283,000)
Pension Plan [Member] | Texas-New Mexico Power Company [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Expected return on plan assets	6.50%	6.80%	7.20%
Expected long-term return on assets decrease resulting in increase net periodic costs In next fiscal year	$ 600,000
Actual rate of return for pension plans	5.50%
Actuarial gains (losses) recorded as regulatory assets	$ (4,960,000)
Other Postretirement Benefits [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Expected long-term return resulting from effect of 1% change	1.00%
Other Postretirement Benefits [Member] | Equity Securities [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Target plan asset allocations	70.00%
Other Postretirement Benefits [Member] | Fixed income [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Target plan asset allocations	30.00%
Other Postretirement Benefits [Member] | Public Service Company of New Mexico [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Expected return on plan assets	7.70%	7.70%	8.50%
Expected long-term return on assets decrease resulting in increase net periodic costs In next fiscal year	$ 700,000
Actual rate of return for pension plans	8.50%
Actuarial gains (losses) recorded as regulatory assets	$ (17,400,000)
Other Postretirement Benefits [Member] | Texas-New Mexico Power Company [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Expected return on plan assets	5.70%	5.70%	6.50%
Expected long-term return on assets decrease resulting in increase net periodic costs In next fiscal year	$ 100,000
Actual rate of return for pension plans	5.50%
Actuarial gains (losses) recorded as regulatory assets	$ 100,000
Effect of 1%-point change in assumed health care cost trend rates on net periodic expense and APBO	0
Estimated future employer contributions in next fiscal year	400,000
Estimated future employer contributions in years two through five	$ 1,400,000