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-Glossary Allowance for Funds Used during Construction

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The component of the allowance for funds used during construction during the period based on an assumed rate of return on equity funds used in financing the construction of regulated assets.

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Summary of the Business and Significant Accounting Policies (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 1986 Operating_Leases	Dec. 31, 2004	Dec. 31, 2003	Dec. 31, 1985 Operating_Leases
Accounting Policies Disclosures [Line Items]
Debt, Weighted Average Interest Rate	6.60%us-gaap_DebtWeightedAverageInterestRate	6.90%us-gaap_DebtWeightedAverageInterestRate	6.60%us-gaap_DebtWeightedAverageInterestRate
Interest costs incurred, capitalized	$ 1.6	$ 1.5	$ 1.2
Public Service Company of New Mexico [Member]
Accounting Policies Disclosures [Line Items]
Allowance for funds used during construction, capitalized interest	4.2	3.3	3.5
Public Utilities, Allowance for Funds Used During Construction, Capitalized Cost of Equity	5.6	4.4	3.8
Interest costs incurred, capitalized	1.1	1.1	0.8
Impairment losses on securities held in the NDT	4.8	3.5	4.8
Texas-New Mexico Power Company [Member]
Accounting Policies Disclosures [Line Items]
Allowance for funds used during construction, capitalized interest	0.5	0.4	0.7
Public Utilities, Allowance for Funds Used During Construction, Capitalized Cost of Equity	0	0	0.6
Interest costs incurred, capitalized	$ 0.1	$ 0	$ 0
Palo Verde Nuclear Generating Station [Member] \| Public Service Company of New Mexico [Member]
Accounting Policies Disclosures [Line Items]
Number of operating leases (in ones)	8			11
EIP Transmission Line [Member] \| Public Service Company of New Mexico [Member]
Accounting Policies Disclosures [Line Items]
Number of operating leases (in ones)							2
Ownership percentage acquired (as a percent)					40.00%	60.00%
10.3% Lessor Notes [Member] \| Public Service Company of New Mexico [Member]
Accounting Policies Disclosures [Line Items]
Notes receivable, stated percentage rate (as a percent)	10.30%
10.15% Lessor Notes [Member] \| Public Service Company of New Mexico [Member]
Accounting Policies Disclosures [Line Items]
Notes receivable, stated percentage rate (as a percent)	10.15%
10.25% EIP Lessor Note Maturing in 2012 [Member] \| EIP Transmission Line [Member] \| Public Service Company of New Mexico [Member]
Accounting Policies Disclosures [Line Items]
Notes receivable, stated percentage rate (as a percent)	10.25%