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Basis of Presentation (Details) $ in Millions | 12 Months Ended
--- | ---
Dec. 31, 2018 USD ($) mi² shares retail_customers | Dec. 31, 2017 USD ($) | Dec. 31, 2016 USD ($)
Basis of Presentation [Abstract] |  |  |
Unrealized Gain (Loss) on Securities | $ |  | $ 2 | $ 5
Service Area Sq Miles | mi² | 4,000 |  |
Incorporated Cities | 51 |  |
Number of Retail Customers | retail_customers | 885,000 |  |
Service area population | 1,900,000 |  |
Percent of State's Population | 46.00% |  |
Entity Number of Employees | 2,967 |  |
Number of Union Employees | 802 |  |
Number of Union Employees Subject to Agreement A | 747 |  |
Number of Union Employees Subject to Agreement B | 55 |  |
Prior Period Reclassification Adjustment | $ | $ 50 | $ (5) | $ (2)

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- Definition Amount of unrealized gain (loss) recognized in the income statement on unsold other securities. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 230 -SubTopic 10 -Section 45 -Paragraph 28 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=109223946&loc=d3e3602-108585 + Details
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