Summary of Business and Significant Accounting Policies (Tables)

12 Months Ended

Dec. 31, 2012

Accounting Policies [Abstract]

Schedule of Inventory, Current [Table Text Block]

Inventories consisted of the following at December 31:

	PNMR				PNM				TNMP
	2012		2011		2012		2011		2012		2011
	(In thousands)
Coal	$	19,231	$	17,175	$	19,231	$	17,175	$	—	$	—
Materials and supplies	40,412		37,056		37,559		34,346		2,853		2,710
	$	59,643	$	54,231	$	56,790	$	51,521	$	2,853	$	2,710

Schedule of Average Rates Used Allocated Between Depreciation Expense and Construction Expense Projects Based on Use of Equipment [Table Text Block]

Average rates used are as follows:

	Year ended December 31
	2012		2011		2010
PNM
Electric plant	2.25	%	2.24	%	2.24	%
Common, intangible, and general plant	5.35	%	6.03	%	5.63	%
TNMP	3.56	%	3.41	%	3.39	%