Financing Short-term Debt (Details) (USD $)	0 Months Ended	12 Months Ended
	Oct. 31, 2011	Dec. 31, 2012 Extensions	Dec. 31, 2011	Dec. 31, 2012 Public Service Company of New Mexico [Member]	Dec. 31, 2011 Public Service Company of New Mexico [Member]	Oct. 31, 2011 Public Service Company of New Mexico [Member]	Dec. 31, 2012 Texas-New Mexico Power Company [Member]	Dec. 31, 2011 Texas-New Mexico Power Company [Member]	Apr. 30, 2009 Texas-New Mexico Power Company [Member]	Dec. 31, 2012 PNMR Term Loan Agreement [Member]	Feb. 22, 2013 Subsequent Event [Member]	Feb. 22, 2013 Subsequent Event [Member] Public Service Company of New Mexico [Member]	Feb. 22, 2013 Subsequent Event [Member] Texas-New Mexico Power Company [Member]	Feb. 22, 2013 Available Borrowing Capacity [Member]
Short-term Debt [Line Items]
Line of Credit Facility, Maximum Borrowing Capacity	$ 300,000,000					$ 400,000,000			$ 75,000,000
Securities Received as Collateral									75,000,000
Line of Credit Facility, Number of Extension Options		2
Line of Credit Facility, Extension Option, Years		1 year
Ratio of debt to capital, maximum (as a percent)	65.00%
Short-term Debt, Weighted Average Interest Rate		1.96%		1.71%						1.335%
Line of Credit Facility, Amount Outstanding		37,600,000	16,700,000	21,100,000	66,000,000		0	0
Line Of Credit Facility Amount Outstanding, Local Institutions			0
Short-term debt		158,700,000	82,700,000	21,100,000	66,000,000					100,000,000
Letters of Credit Outstanding, Amount		11,300,000		3,500,000			300,000
Line of Credit Facility, Remaining Borrowing Capacity											264,500,000	288,800,000	49,700,000	603,000,000
Invested Cash and Cash Equivalents											$ 2,800,000