XML 65 R51.htm IDEA: XBRL DOCUMENT
v3.10.0.1

Regulatory Matters - Electric Rates (Details) $ in Millions |  |  |  |  |  | 1 Months Ended | 3 Months Ended | 6 Months Ended | 12 Months Ended
--- | --- | --- | --- | --- | --- | --- | --- | --- | ---
May 25, 2018 USD ($) | Apr. 02, 2018 USD ($) | Jan. 18, 2018 USD ($) | Aug. 09, 2017 | Apr. 13, 2017 USD ($) | Dec. 31, 2016 USD ($) | Nov. 30, 2016 USD ($) | Jun. 30, 2018 USD ($) Customers Years MW | Jun. 30, 2017 USD ($) | Jun. 30, 2018 USD ($) Customers Years MW | Jun. 30, 2017 USD ($) | Dec. 31, 2017 USD ($)
Regulatory Matters [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Pre-Tax Charge to Fuel, Purchase Power and Gas - Utility |  |  |  |  |  |  |  | $ 96.5 | $ 93.1 | $ 197.4 | $ 189.7 |
MPUC [Member] | 2016 Minnesota General Rate Case [Member] | Minnesota Power [Member] |  |  |  |  |  |  |  |  |  |  |  |
Regulatory Matters [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Pre-Tax Charge to Fuel, Purchase Power and Gas - Utility |  |  |  |  |  |  |  |  |  |  |  | $ 19.5
MPUC [Member] | 2016 Minnesota General Rate Case [Member] | Minnesota Power [Member] | Boswell Energy Center [Member] |  |  |  |  |  |  |  |  |  |  |  |
Regulatory Matters [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Expected Decrease in Annual Depreciation Expense |  |  |  |  |  |  |  | 25.0 |  | 25.0 |  |
PSCW [Member] | 2016 Wisconsin General Rate Case [Member] | SWL&P [Member] | Retail Customers [Member] |  |  |  |  |  |  |  |  |  |  |  |
Regulatory Matters [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Approved Return on Common Equity |  |  |  | 10.50% |  |  |  |  |  |  |  |
Approved Equity Ratio |  |  |  | 55.00% |  |  |  |  |  |  |  |
Expected Annualized Collection of Additional Revenue Under Retail Rate Order |  |  |  |  |  |  |  |  |  | $ 2.5 |  |
PSCW [Member] | 2012 Wisconsin Rate Case [Member] | SWL&P [Member] | Retail Customers [Member] |  |  |  |  |  |  |  |  |  |  |  |
Regulatory Matters [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Approved Return on Common Equity |  |  |  |  |  |  |  |  |  | 10.90% |  |
PSCW [Member] | 2018 Wisconsin General Rate Case [Member] | SWL&P [Member] | Retail Customers [Member] |  |  |  |  |  |  |  |  |  |  |  |
Regulatory Matters [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Requested Average Rate Increase | 2.70% |  |  |  |  |  |  |  |  |  |  |
Requested Return on Equity | 10.50% |  |  |  |  |  |  |  |  |  |  |
Requested Equity Ratio | 55.41% |  |  |  |  |  |  |  |  |  |  |
Annual Additional Revenue Generated from Requested Final Rate Increase | $ 2.4 |  |  |  |  |  |  |  |  |  |  |
Electric Rates [Member] | MPUC [Member] | Minnesota Cost Recovery Riders [Member] | Minnesota Power [Member] | Retail Customers [Member] |  |  |  |  |  |  |  |  |  |  |  |
Regulatory Matters [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Revenue from Cost Recovery Riders |  |  |  |  |  |  |  | 28.0 | 24.4 | $ 52.1 | 48.6 |
Electric Rates [Member] | MPUC [Member] | 2016 Minnesota General Rate Case [Member] | Minnesota Power [Member] | Retail Customers [Member] |  |  |  |  |  |  |  |  |  |  |  |
Regulatory Matters [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Requested Average Rate Increase |  |  |  |  |  |  | 9.00% |  |  |  |  |
Requested Return on Equity |  |  |  |  |  |  | 10.25% |  |  |  |  |
Requested Equity Ratio |  |  |  |  |  |  | 53.81% |  |  |  |  |
Annual Additional Revenue Generated from Requested Final Rate Increase |  |  | $ 13.0 |  |  |  | $ 55.0 |  |  |  |  |
Annual Additional Revenue Generated from Requested Interim Rate Increase |  |  |  |  | $ 32.2 | $ 34.7 | 49.0 |  |  |  |  |
Annual Additional Revenue Generated from Requested Final Rate Increase, Amended |  |  |  |  |  |  | $ 49.0 |  |  |  |  |
Approved Return on Common Equity |  |  | 9.25% |  |  |  |  |  |  |  |  |
Approved Equity Ratio |  |  | 53.81% |  |  |  |  |  |  |  |  |
Reserve for Interim Rate Refund |  |  |  |  |  |  |  | 49.2 |  | 49.2 |  | 32.3
Electric Rates [Member] | MPUC [Member] | 2016 Minnesota General Rate Case [Member] | Minnesota Power [Member] | Retail Customers [Member] | Minimum [Member] |  |  |  |  |  |  |  |  |  |  |  |
Regulatory Matters [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Requested Reconsideration of Certain Decisions Representing Annualized Additional Revenue |  | $ 20.0 |  |  |  |  |  |  |  |  |  |
Electric Rates [Member] | MPUC [Member] | 2016 Minnesota General Rate Case [Member] | Minnesota Power [Member] | Retail Customers [Member] | Maximum [Member] |  |  |  |  |  |  |  |  |  |  |  |
Regulatory Matters [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Requested Reconsideration of Certain Decisions Representing Annualized Additional Revenue |  | $ 25.0 |  |  |  |  |  |  |  |  |  |
Electric Rates [Member] | MPUC [Member] | Energy-Intensive Trade-Exposed Customer Rates [Member] | Minnesota Power [Member] | Retail Customers [Member] |  |  |  |  |  |  |  |  |  |  |  |
Regulatory Matters [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Provided Discounts to EITE Customers |  |  |  |  |  |  |  | 3.8 | $ 3.6 | 8.1 | $ 5.9 | $ 8.6
Expected Discounts to EITE Customers Annually |  |  |  |  |  |  |  | $ 15.0 |  | $ 15.0 |  |
Electric Rates [Member] | FERC [Member] | FERC-Approved Wholesale Rates [Member] | Minnesota Power [Member] | Municipal Customers [Member] |  |  |  |  |  |  |  |  |  |  |  |
Regulatory Matters [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Number of Customers | Customers |  |  |  |  |  |  |  | 16 |  | 16 |  |
Length of Notice Required to Terminate (Years) | Years |  |  |  |  |  |  |  | 3 |  | 3 |  |
Electric Rates [Member] | FERC [Member] | FERC-Approved Wholesale Rates [Member] | Minnesota Power [Member] | Municipal Customers [Member] | Wholesale Electric Contract (Termination Effective June 2019) [Member] |  |  |  |  |  |  |  |  |  |  |  |
Regulatory Matters [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Average Monthly Demand (MW) | MW |  |  |  |  |  |  |  | 29 |  | 29 |  |
Electric Rates [Member] | FERC [Member] | FERC-Approved Wholesale Rates [Member] | Minnesota Power [Member] | Municipal Customers [Member] | Wholesale Electric Contract (Cost-Based Formula Methodology for Entire Term) [Member] |  |  |  |  |  |  |  |  |  |  |  |
Regulatory Matters [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Number of Customers | Customers |  |  |  |  |  |  |  | 3 |  | 3 |  |
Electric Rates [Member] | FERC [Member] | FERC-Approved Wholesale Rates [Member] | Minnesota Power [Member] | Municipal Customers [Member] | Wholesale Electric Contracts (Expire from 2024 through 2029) [Member] |  |  |  |  |  |  |  |  |  |  |  |
Regulatory Matters [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Number of Customers | Customers |  |  |  |  |  |  |  | 14 |  | 14 |  |
Electric Rates [Member] | PSCW [Member] | 2018 Wisconsin General Rate Case [Member] | SWL&P [Member] | Retail Customers [Member] |  |  |  |  |  |  |  |  |  |  |  |
Regulatory Matters [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Requested Average Rate Increase | 2.00% |  |  |  |  |  |  |  |  |  |  |
Natural Gas [Member] | PSCW [Member] | 2018 Wisconsin General Rate Case [Member] | SWL&P [Member] | Retail Customers [Member] |  |  |  |  |  |  |  |  |  |  |  |
Regulatory Matters [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Requested Average Rate Increase | 2.30% |  |  |  |  |  |  |  |  |  |  |
Water [Member] | PSCW [Member] | 2018 Wisconsin General Rate Case [Member] | SWL&P [Member] | Retail Customers [Member] |  |  |  |  |  |  |  |  |  |  |  |
Regulatory Matters [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Requested Average Rate Increase | 8.30% |  |  |  |  |  |  |  |  |  |  |

X
- Definition Average demand measured for a specified customer, measured in MW. + References No definition available. + Details
Name: | ale_AverageCustomerDemandMW
Namespace Prefix: | ale_
Data Type: | num:powerItemType
Balance Type: | na
Period Type: | instant

X
- Definition Discount Provided to EITE Customers + References No definition available. + Details
Name: | ale_DiscountProvidedtoEITECustomers
Namespace Prefix: | ale_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- Definition Estimated Discount to be Provided During the Next Twelve Months + References No definition available. + Details
Name: | ale_EstimatedDiscounttobeProvidedDuringtheNextTwelveMonths
Namespace Prefix: | ale_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition Fuel, Purchased Power and Gas - Utility + References No definition available. + Details
Name: | ale_FuelPurchasedPowerandGasUtility
Namespace Prefix: | ale_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- Definition Increase (Decrease) in Annual Depreciation Expense Based on Regulatory Order + References No definition available. + Details
Name: | ale_IncreaseDecreaseinAnnualDepreciationExpenseBasedonRegulatoryOrder
Namespace Prefix: | ale_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition The length of notice required to terminate a contract (in years). + References No definition available. + Details
Name: | ale_LengthOfNoticeRequiredToTerminateYears
Namespace Prefix: | ale_
Data Type: | xbrli:integerItemType
Balance Type: | na
Period Type: | instant

X
- Definition Number of Customers + References No definition available. + Details
Name: | ale_NumberOfCustomers
Namespace Prefix: | ale_
Data Type: | xbrli:integerItemType
Balance Type: | na
Period Type: | instant

X
- Definition Public Utilities, Approved Rate Increase (Decrease), Reconsideration Amount + References No definition available. + Details
Name: | ale_PublicUtilitiesApprovedRateIncreaseDecreaseReconsiderationAmount
Namespace Prefix: | ale_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

X
- Definition Reserve for Interim Rate Refund + References No definition available. + Details
Name: | ale_ReserveforInterimRateRefund
Namespace Prefix: | ale_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition Percentage of public utility's approved equity to capital, including debt and equity. + References No definition available. + Details
Name: | us-gaap_PublicUtilitiesApprovedEquityCapitalStructurePercentage
Namespace Prefix: | us-gaap_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | duration

X
- Definition Amount of public utility's approved rate increase (decrease) by regulatory agency. + References No definition available. + Details
Name: | us-gaap_PublicUtilitiesApprovedRateIncreaseDecreaseAmount
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

X
- Definition Percentage of public utility's approved return on equity. + References No definition available. + Details
Name: | us-gaap_PublicUtilitiesApprovedReturnOnEquityPercentage
Namespace Prefix: | us-gaap_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | duration

X
- Definition Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table. + References No definition available. + Details
Name: | us-gaap_PublicUtilitiesGeneralDisclosuresLineItems
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

X
- Definition Amount of public utility's interim rate increase (decrease) allowed while waiting final decision of regulatory agency. + References No definition available. + Details
Name: | us-gaap_PublicUtilitiesInterimRateIncreaseDecreaseAmount
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

X
- Definition Percentage of public utility's requested equity to capital, including debt and equity. + References No definition available. + Details
Name: | us-gaap_PublicUtilitiesRequestedEquityCapitalStructurePercentage
Namespace Prefix: | us-gaap_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | duration

X
- Definition Amount of public utility's amended requested rate increase (decrease) with regulatory agency. + References No definition available. + Details
Name: | us-gaap_PublicUtilitiesRequestedRateIncreaseDecreaseAmendedAmount
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

X
- Definition Amount of public utility's requested rate increase (decrease) with regulatory agency. + References No definition available. + Details
Name: | us-gaap_PublicUtilitiesRequestedRateIncreaseDecreaseAmount
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

X
- Definition Percentage of public utility's requested rate increase (decrease) with regulatory agency. + References No definition available. + Details
Name: | us-gaap_PublicUtilitiesRequestedRateIncreaseDecreasePercentage
Namespace Prefix: | us-gaap_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | duration

X
- Definition Percentage of public utility's requested return on equity. + References No definition available. + Details
Name: | us-gaap_PublicUtilitiesRequestedReturnOnEquityPercentage
Namespace Prefix: | us-gaap_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | duration

X
- Definition The amount of regulated other operating revenues recognized during the period. + References No definition available. + Details
Name: | us-gaap_RegulatedOperatingRevenueOther
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

X
- Details
Name: | us-gaap_RegulatoryAgencyAxis=ale_MPUCMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_PublicUtilitiesRegulatoryProceedingAxis=ale_A2016MinnesotaRateCaseMemberMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | dei_LegalEntityAxis=ale_MinnesotaPowerMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | ale_GeneratingFacilityAxisAxis=ale_BoswellEnergyCenterMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_RegulatoryAgencyAxis=ale_PSCWMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_PublicUtilitiesRegulatoryProceedingAxis=ale_A2016WisconsinRateCaseMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | dei_LegalEntityAxis=ale_SWLPMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | ale_CustomerClassAxis=ale_RetailCustomersMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_PublicUtilitiesRegulatoryProceedingAxis=ale_A2012WisconsinRateCaseMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_PublicUtilitiesRegulatoryProceedingAxis=ale_A2018WisconsinGeneralRateCaseMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | ale_RateTypeAxis=ale_ElectricRatesMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_PublicUtilitiesRegulatoryProceedingAxis=ale_CurrentCostRecoveryRiderMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | srt_RangeAxis=srt_MinimumMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | srt_RangeAxis=srt_MaximumMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_PublicUtilitiesRegulatoryProceedingAxis=ale_EnergyIntensiveTradeExposedCustomerRatesMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_RegulatoryAgencyAxis=ale_FERCMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_PublicUtilitiesRegulatoryProceedingAxis=ale_FercApprovedWholesaleRatesMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | ale_CustomerClassAxis=ale_MunicipalCustomersMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | ale_LongtermContractsforSaleofElectricPowerAxis=ale_WholesaleElectricContractTerminationEffectiveJune2019Member
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | ale_LongtermContractsforSaleofElectricPowerAxis=ale_WholesaleElectricContractCostBasedFormulaMethodologyforEntireTermMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | ale_LongtermContractsforSaleofElectricPowerAxis=ale_WholesaleElectricContractsExpirefrom2024through2029Member
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | ale_RateTypeAxis=srt_NaturalGasReservesMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | ale_RateTypeAxis=us-gaap_PublicUtilitiesInventoryWaterMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |