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Basis of Presentation (Details) $ in Millions | 12 Months Ended
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Dec. 31, 2020 USD ($) mi² shares retail_customers | Dec. 31, 2019 USD ($) | Dec. 31, 2018 USD ($)
Basis of Presentation [Abstract] |  |  |
Service Area Sq Miles | mi² | 4,000,000 |  |
Incorporated Cities | 51 |  |
Number of Retail Customers | retail_customers | 908,000 |  |
Service area population | 1,900,000 |  |
Entity Number of Employees | 3,639 |  |
Number of Union Employees | 721 |  |
Number of Union Employees Subject to Agreement A | 660 |  |
Number of Union Employees Subject to Agreement B | 61 |  |
Share-based Payment Arrangement, Noncash Expense | $ | $ 11 | $ 9 | $ 5

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- Definition Approximate square miles of service area. + References No definition available. + Details
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- Definition Amount of noncash expense for share-based payment arrangement. + 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 (a) -URI http://asc.fasb.org/extlink&oid=121586364&loc=d3e3602-108585 + Details
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