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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

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