Basis of Presentation (Details) shares in Millions, $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2015 USD ($) mi² retail_customers shares	Sep. 30, 2014 USD ($)	Sep. 30, 2015 USD ($) mi² retail_customers shares	Sep. 30, 2014 USD ($)
Basis of Presentation [Abstract]
Service Area Sq Miles | mi²	4,000		4,000
Incorporated Cities	52		52
Number of Retail Customers | retail_customers	851,650		851,650
Service Area Population | shares	1.8		1.8
Percent of State's Population	46.00%		46.00%
Increase (Decrease) in Inventories			$ (12)	$ (18)
Other Comprehensive Income	$ 0	$ 0	$ 0	$ 0