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Basis of Presentation (Details) retail_customers in Thousands, mi² in Thousands, $ in Millions | 3 Months Ended | 6 Months Ended
--- | --- | ---
Jun. 30, 2018 USD ($) mi² retail_customers | Jun. 30, 2017 USD ($) | Jun. 30, 2018 USD ($) mi² retail_customers | Jun. 30, 2017 USD ($)
Basis of Presentation [Abstract] |  |  |  |
Service Area Sq Miles | mi² | 4 |  | 4 |
Incorporated Cities | 51 |  | 51 |
Number of Retail Customers | retail_customers | 883 |  | 883 |
Percent of state population | 46.00% |  | 46.00% |
Defined Benefit Plan, Non-service Cost | $ 2 | $ 1 | $ 3 | $ 2
Alternative revenue programs, net of amortization | 0 | 0 | 2 | 0
Revenues | 449 | $ 449 | 942 | $ 979
Defined Benefit Plan, Expected Amortization of Prior Service Cost (Credit), Next Fiscal Year | 3 |  | 3 |
Pension and Other Postretirement Plans Costs [Member] |  |  |  |
Defined Benefit Plan, Non-service Cost | $ 1 |  | $ 2 |

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- Definition Number of incorporated cities in service area. + References No definition available. + Details
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- Definition Includes residential, commercial and industrial. + References No definition available. + Details
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- Definition Amount included in accumulated other comprehensive (income) loss for prior service cost (credit) expected to be recognized in net periodic benefit cost (credit) for fiscal year following most recent annual statement of financial position. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (s) -URI http://asc.fasb.org/extlink&oid=82843861&loc=d3e1928-114920 + Details
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- Definition Amount of revenue recognized from goods sold, services rendered, insurance premiums, or other activities that constitute an earning process. Includes, but is not limited to, investment and interest income before deduction of interest expense when recognized as a component of revenue, and sales and trading gain (loss). + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 225 -SubTopic 10 -Section S99 -Paragraph 2 -Subparagraph (SX 210.5-03.1) -URI http://asc.fasb.org/extlink&oid=63488584&loc=d3e20235-122688 + Details
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