Regulatory matters	9 Months Ended
Regulatory matters	Sep. 30, 2021
Regulated Operations [Abstract]
Regulatory Matters	Regulatory matters The Company regularly reviews the need for electric and natural gas rate changes in each of the jurisdictions in which service is provided. The Company files for rate adjustments to seek recovery of operating costs and capital investments, as well as reasonable returns as allowed by regulators. Certain regulatory proceedings and cases may also contain recurring mechanisms that can have an annual true-up. Examples of these recurring mechanisms include: infrastructure riders, transmission trackers, renewable resource cost adjustment riders, as well as weather normalization and decoupling mechanisms. The following paragraphs summarize the Company's significant open regulatory proceedings and cases by jurisdiction including updates to those reported in the 2020 Annual Report. The Company is unable to predict the ultimate outcome of these matters, the timing of final decisions of the various regulators and courts, or the effect on the Company's results of operations, financial position or cash flows. IPUC On January 12, 2021, Intermountain filed an application with the IPUC for a decrease in its depreciation and amortization rates of approximately $2.9 million annually or a decrease from a combined rate of 3.0 percent to 2.6 percent. On June 3, 2021, Intermountain filed a joint settlement agreement with the IPUC Staff reflecting a revised annual decrease of approximately $3.8 million or approximately 2.4 percent. On August 18, 2021, the settlement agreement was approved with rates retroactive to January 1, 2021. MNPUC Great Plains defers the difference between the actual cost of gas spent to serve customers and that recovered from customers on a monthly basis. Annually, Great Plains prepares a true-up pursuant to the purchased gas adjustment tariff. On August 30, 2021, the MNPUC issued an order to allow Great Plains recovery of an out-of-cycle cost of gas adjustment of $8.8 million over a period of 27 months. The order was effective September 1, 2021, and is subject to a prudence review by the MNPUC. The requested increase was for the February 2021 extreme cold weather, primarily in the central United States, and market conditions surrounding the natural gas commodity market. The MNPUC prudence review is pending with an order to be issued on or before August 29, 2022. NDPSC On July 15, 2021, Montana-Dakota filed an annual update to its transmission cost adjustment rider with the NDPSC requesting to recover revenues of approximately $14.5 million, which includes a true-up of the prior period adjustment, resulting in a decrease of approximately $1.1 million from current rates. This filing includes approximately $5.1 million related to transmission capital projects. On September 22, 2021, the NDPSC approved the decrease with rates effective November 1, 2021. SDPUC On August 19, 2020, the SDPUC approved the use of deferred accounting by Montana-Dakota to track expenses and revenues related to the COVID-19 pandemic. Montana-Dakota has determined the deferred accounting order was not necessary as no costs were recorded as regulatory assets. The filing was withdrawn by Montana-Dakota on July 30, 2021. On March 11, 2021, Montana-Dakota filed an informational update to the infrastructure rider rate tariff with the SDPUC related to the retirement of Unit 1 at Lewis & Clark Station. The filing includes the annual revenue requirement offset by the related amortization of the accelerated depreciation on the plant, net of excess deferred income taxes, and the decommissioning costs projected to be incurred in 2021 resulting in no impact to customers. This matter is pending before the SDPUC. WUTC On June 1, 2021, Cascade filed its annual pipeline cost recovery mechanism requesting an increase in annual revenue of approximately $2.1 million or approximately 0.8 percent. On October 15, 2021, Cascade filed an update reflecting a revised increase in annual revenue of approximately $1.7 million, or approximately 0.6 percent, which includes actual costs as of September 30, 2021. On October 28, 2021, the filing was approved with rates effective November 1, 2021. On September 30, 2021, Cascade filed an application with the WUTC for a natural gas rate increase of approximately $13.7 million annually or approximately 5.1 percent above current rates. The requested increase was primarily to recover investments made in infrastructure upgrades, as well as to recover 2021 wage increases. The WUTC has 11 months to render a final decision on the rate case. This matter is pending before the WUTC. FERC On September 1, 2021, Montana-Dakota filed an update to its transmission formula rate under the MISO tariff for its multi-value project for $13.4 million, which is effective January 1, 2022.