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Regulatory Matters (Tables) | 12 Months Ended
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Dec. 31, 2018
Regulated Operations [Abstract] |
Regulatory Assets and Liabilities [Table Text Block] |
Regulatory Assets and Liabilities |  |
As of December 31 | 2018 |  | 2017 |
Millions |  |
Non-Current Regulatory Assets |  |
Defined Benefit Pension and Other Postretirement Benefit Plans (b) |  | $218.5 |  |  | $220.3 |
Income Taxes (c) | 105.5 |  | 112.8 |
Asset Retirement Obligations (d) | 32.6 |  | 29.6 |
Boswell 1 & 2 (l) | 16.3 |  | — |
Manufactured Gas Plant (e) | 8.0 |  | 8.1 |
PPACA Income Tax Deferral | 5.0 |  | 5.0 |
Conservation Improvement Program (f) | — |  | 3.3 |
Other | 3.6 |  | 5.6 |
Total Non-Current Regulatory Assets |  | $389.5 |  |  | $384.7 |
Current Regulatory Liabilities (a) |  |
Provision for Interim Rate Refund (i) |  | $40.0 |  | — |
Provision for Tax Reform Refund (j) | 10.7 |  | — |
Transmission Formula Rates | 4.4 |  | — |
Total Current Regulatory Liabilities | 55.1 |  | — |
Non-Current Regulatory Liabilities |  |
Income Taxes (c) | 396.4 |  |  | $411.2 |
Wholesale and Retail Contra AFUDC (h) | 64.4 |  | 57.9 |
Provision for Interim Rate Refund (i) | — |  | 23.7 |
Plant Removal Obligations | 25.1 |  | 20.3 |
North Dakota Investment Tax Credits (k) | 14.7 |  | 14.1 |
Cost Recovery Riders (g) | 6.9 |  | 2.2 |
Transmission Formula Rates | 1.6 |  | — |
Other | 3.0 |  | 2.6 |
Total Non-Current Regulatory Liabilities | 512.1 |  | 532.0 |
Total Regulatory Liabilities |  | $567.2 |  |  | $532.0 |
(a) | Current regulatory liabilities are presented within Other Current Liabilities on the Consolidated Balance Sheet.
(b) | Defined benefit pension and other postretirement items included in our Regulated Operations, which are otherwise required to be recognized in accumulated other comprehensive income as actuarial gains and losses as well as prior service costs and credits, are recognized as regulatory assets or regulatory liabilities on the Consolidated Balance Sheet. The asset or liability will decrease as the deferred items are amortized and recognized as components of net periodic benefit cost. (See Note 15. Pension and Other Postretirement Benefit Plans.)
(c) | These costs represent the difference between deferred income taxes recognized for financial reporting purposes and amounts previously billed to our customers. The balances will primarily decrease over the remaining life of the related temporary differences and flow through current income taxes.
(d) | Asset retirement obligations will accrete and be amortized over the lives of the related property with asset retirement obligations.
(e) | The manufactured gas plant regulatory asset represents costs of remediation for a former manufactured gas plant site located in Superior, Wisconsin, and formerly operated by SWL&P. We expect recovery of these remediation costs to be allowed by the PSCW in rates over time.
(f) | The conservation improvement program regulatory asset represents CIP expenditures, any financial incentive earned for cost-effective program achievements and a carrying charge deferred for future cost recovery over the next year following MPUC approval.
(g) | The cost recovery rider regulatory liabilities are cash collections from our customers in excess of revenue recognized, primarily due to capital expenditures related to Bison, investment in CapX2020 projects, the Boswell Unit 4 environmental upgrade and the GNTL. The cost recovery rider regulatory liabilities as of December 31, 2018, will be returned within the next two years.
(h) | Wholesale and retail contra AFUDC represents amortization to offset AFUDC Equity and Debt recorded during the construction period of our cost recovery rider projects prior to placing the projects in service. The regulatory liability will decrease over the remaining depreciable life of the related asset.
(i) | This amount is expected to be refunded to Minnesota Power’s regulated retail customers in 2019 and includes $23.8 million of discounts provided to EITE customers as of December 31, 2018, that will be offset against interim rate refunds ($8.6 million as of December 31, 2017). (See 2016 Minnesota General Rate Case and Energy-Intensive Trade‑Exposed Customer Rates.)
(j) | Provision for tax reform refund is expected to be refunded to Minnesota Power customers in the first quarter of 2019 and SWL&P customers in 2019 and 2020. (See Tax Cuts and Jobs Act of 2017.)
(k) | North Dakota investment tax credits expected to be realized from Bison that will be credited to Minnesota Power’s regulated retail customers through future renewable cost recovery rider filings as the tax credits are utilized.
(l) | In December 2018, Minnesota Power retired Boswell Units 1 and 2 and reclassified the remaining net book value from property, plant and equipment to a regulatory asset on the Consolidated Balance Sheet. The remaining net book value is currently included in Minnesota Power’s rate base and Minnesota Power is earning a return on the outstanding balance.

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