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Summary of the Business and Significant Accounting Policies - Narrative (Details)	12 Months Ended
	Dec. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)	Dec. 31, 2014 USD ($)	Jan. 01, 2017 USD ($)	Dec. 31, 1986 lease
Accounting Policies Disclosures [Line Items]
Payment defaults	$ 0
Unrealized gains, net of income taxes, recorded in AOCI	3,800,000
Allowance for equity funds used during construction	$ 4,949,000	$ 10,430,000	$ 5,563,000
Weighted average borrowing rate	6.10%	6.60%	6.60%
Interest costs incurred, capitalized	$ 1,800,000	$ 1,500,000	$ 1,600,000
Subsequent Event [Member] | Accounting Standards Update 2016-09 [Member]
Accounting Policies Disclosures [Line Items]
Reduction of accumulated deferred income tax liabilities				$ 8,400,000
Subsequent Event [Member] | Accounting Standards Update 2016-09 [Member] | Retained Earnings [Member]
Accounting Policies Disclosures [Line Items]
Increase in retained earnings				$ 8,400,000
Public Service Company of New Mexico [Member]
Accounting Policies Disclosures [Line Items]
Allowance for funds used during construction, capitalized interest	5,300,000	7,800,000	4,200,000
Allowance for equity funds used during construction	4,163,000	10,430,000	5,563,000
Interest costs incurred, capitalized	800,000	800,000	1,100,000
Impairment losses on securities held in the NDT	$ 13,900,000	10,400,000	4,800,000
Public Service Company of New Mexico [Member] | 10.3% Lessor Notes [Member]
Accounting Policies Disclosures [Line Items]
Notes receivable, stated percentage rate	10.30%
Public Service Company of New Mexico [Member] | 10.15% Lessor Notes [Member]
Accounting Policies Disclosures [Line Items]
Notes receivable, stated percentage rate	10.15%
Public Service Company of New Mexico [Member] | Palo Verde Nuclear Generating Station [Member]
Accounting Policies Disclosures [Line Items]
Number of operating leases | lease					11
Texas-New Mexico Power Company [Member]
Accounting Policies Disclosures [Line Items]
Allowance for funds used during construction, capitalized interest	$ 900,000	500,000	500,000
Allowance for equity funds used during construction	800,000	0	0
Interest costs incurred, capitalized	$ 100,000	$ 100,000	$ 100,000

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