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Basis of Presentation (Details) retail_customers in Thousands, mi² in Thousands, $ in Millions | 3 Months Ended | 9 Months Ended
--- | --- | ---
Sep. 30, 2018 USD ($) mi² retail_customers | Sep. 30, 2017 USD ($) | Sep. 30, 2018 USD ($) mi² retail_customers | Sep. 30, 2017 USD ($)
Basis of Presentation [Abstract] |  |  |  |
Service Area Sq Miles | mi² | 4 |  | 4 |
Incorporated Cities | 51 |  | 51 |
Number of Retail Customers | retail_customers | 885 |  | 885 |
Percent of state population | 46.00% |  | 46.00% |
Alternative revenue programs, net of amortization | $ 0 | $ 0 | $ (2) | $ 0
Defined Benefit Plan, Non-service Cost | 1 | 1 | 4 | 3
Revenues | 525 | $ 515 | 1,467 | $ 1,494
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 |  |  | $ 2 |

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- Definition Amount of increase (decrease) in revenue recognized for cumulative catch-up adjustment from change in estimate of transaction price which (increases) decreases obligation to transfer good or service to customer for which consideration from customer has been received or is due. Includes, but is not limited to, change in assessment of whether estimate of variable consideration is constrained. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 606 -SubTopic 10 -Section 50 -Paragraph 10 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=109196051&loc=SL49130551-203045 + Details
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