Commitments, Contingencies and Uncertainties (Narrative) (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended	0 Months Ended				0 Months Ended	12 Months Ended	0 Months Ended
	Dec. 31, 2013	May 23, 2013 Four Corners Coal Plant Participants	May 23, 2013 Four Corners Generating Station	Dec. 31, 2013 Minimum	Dec. 31, 2013 Four Corners Generating Station	Feb. 14, 2014 Four Corners Generating Station	Dec. 31, 2013 Four Corners Generating Station	Feb. 14, 2014 Scenario, Forecast Four Corners Generating Station
Mercury and Air Toxics Standards Required Compliance Period, in Years				3 years
Cost of Pollution Control Equipment					$ 39
Accrual for Environmental Loss Contingencies	0.5
Public Utilities, Assessed Coal Severance Surtax Penalty and Interest		$ 30.0	$ 1.5
Number of criteria emissions established under the Clear Air Act	6
Frequency of Review by Environmental Protection Agency	5 years
Date participation is ceased							Jul. 06, 2016
GHG Emission Level	17.00%
Comment period	60 days
Stay Of Judicial Proceeding Period						30 days
Stay Of Judicial Proceeding, Due Date								Mar. 17, 2014