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Basis of Presentation (Details) $ in Millions | 12 Months Ended |
--- | --- | ---
Dec. 31, 2016 USD ($) | Dec. 31, 2015 USD ($) | Dec. 31, 2017 mi² shares retail_customers
Basis of Presentation [Abstract] |  |  |
Service Area Sq Miles | mi² |  |  | 4,000
Incorporated Cities |  |  | 51
Number of Retail Customers | retail_customers |  |  | 875,000
Service area population |  |  | 1,900,000
Percent of State's Population |  |  | 46.00%
Entity Number of Employees |  |  | 2,906
Number of Union Employees |  |  | 785
Number of Union Employees Subject to Agreement A |  |  | 732
Number of Union Employees Subject to Agreement B |  |  | 53
Cash received to be returned to customers pursuant to the Residential Exchange Program | $ | $ 6 | $ 1 |
Contribution to the voluntary employees’ beneficiary association trust | $ | 2 | 4 |
Regulatory deferral of settled derivative instruments | $ | $ 2 | $ 2 |

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- Definition The amount of cash or cash equivalents contributed during the reporting period by the entity to fund its non-pension postretirement benefit plans. + References No definition available. + Details
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- Definition Gain (loss) related to the termination of a contract between the parties. The termination may be due to many causes including early termination of a lease by a lessee, a breach of contract by one party, or a failure to perform. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 420 -SubTopic 10 -Section 50 -Paragraph 1 -Subparagraph (b)(1) -URI http://asc.fasb.org/extlink&oid=6394359&loc=d3e17939-110869 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 230 -SubTopic 10 -Section 45 -Paragraph 28 -URI http://asc.fasb.org/extlink&oid=98514028&loc=d3e3602-108585 + Details
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