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Basis of Presentation (Details) (USD $)
In Millions, unless otherwise specified
 3 Months Ended 9 Months Ended 12 Months Ended
Sep. 30, 2014
sqmi
retail_customers
Sep. 30, 2013
Jun. 30, 2013
Sep. 30, 2014
sqmi
retail_customers
Sep. 30, 2013
Dec. 31, 2012
Dec. 31, 2011
Dec. 31, 2010
Dec. 31, 2009
Dec. 31, 2013
Basis of Presentation [Abstract]                    
Service Area Sq Miles 4,000     4,000            
Incorporated Cities 52     52            
Number of Retail Customers 843,110     843,110            
Service Area Population 1.7     1.7            
Percent of State's Population 44.00%     44.00%            
Margin Deposit Assets $ 5     $ 5           $ 9
Power Cost Deferrals, Net         4          
Other Comprehensive Income 0 0   0 0          
Revenue overstatement     $ 9     $ 3 $ 3 $ 2 $ 1