Basis of Presentation (Details) (USD $) In Millions, except Share data, unless otherwise specified	12 Months Ended
	Dec. 31, 2012 sqmi	Dec. 31, 2011	Dec. 31, 2010
Basis of Presentation [Abstract]
Incorporated Cities	52
Service Area Sq Miles	4,000
Number of Retail Customers	828,354
Service area population	1,700,000
Percent of State's Population	44.00%
Entity Number of Employees	2,603
Number of Union Employees	809
Number of Union Employees Subject to Agreement A	775
Number of Union Employees Subject to Agreement B	34
Other Accrued Liabilities, Current		$ 6
Pension and Other Postretirement Benefit Expense	27	15	11
Senate Bill 408 deferrals, net		$ 7	$ 13