Commitments, Contingencies And Uncertainties (Narrative) (Details)			9 Months Ended
	Jul. 06, 2016	Apr. 22, 2016 Countries	Sep. 30, 2016 Decimals	Jul. 28, 2015 States
Loss Contingencies [Line Items]
Number of States Affected by EPA's Emissions Budgets | States				13
Number of criteria emissions established under the Clear Air Act			6
Frequency of Review by Environmental Protection Agency			5 years
Jointly Owned Utility Plant, Proportionate Ownership Share	7.00%
Number of countries that signed the Paris Agreement | Countries		175
Frequency of Review by Countries Participating in the Paris Agreement		5 years
Four Corners Generating Station
Loss Contingencies [Line Items]
Date participation is ceased	Jul. 06, 2016
Minimum
Loss Contingencies [Line Items]
Public Utilities, Government Standard Emission Limit			70
Maximum
Loss Contingencies [Line Items]
Public Utilities, Government Standard Emission Limit			75