XML 65 R51.htm IDEA: XBRL DOCUMENT
v3.8.0.1

Regulatory Matters - Electric Rates (Details) $ in Millions |  |  | 1 Months Ended | 3 Months Ended | 9 Months Ended
--- | --- | --- | --- | --- | ---
Aug. 09, 2017 USD ($) | Apr. 13, 2017 USD ($) | Dec. 31, 2016 USD ($) | Nov. 30, 2016 USD ($) | Jun. 30, 2016 | Sep. 30, 2017 USD ($) Customers Years MW | Sep. 30, 2016 USD ($) | Sep. 30, 2017 USD ($) Customers Years MW | Sep. 30, 2016 USD ($)
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% |  |  |  |  |  |  |  |
Requested Average Rate Increase |  |  |  |  | 3.10% |  |  |  |
Requested Return on Equity |  |  |  |  | 10.90% |  |  |  |
Requested Equity Ratio |  |  |  |  | 55.00% |  |  |  |
Revenue Increase (Decrease) from Approved Rate | $ 2.5 |  |  |  |  |  |  |  |
Approved Rate Increase (Decrease) | 2.90% |  |  |  |  |  |  |  |
Electric Rates [Member] | MPUC [Member] | 2010 Minnesota Rate Case [Member] | Minnesota Power [Member] | Retail Customers [Member] |  |  |  |  |  |  |  |  |
Regulatory Matters [Line Items] |  |  |  |  |  |  |  |  |
Approved Return on Common Equity |  |  |  |  |  |  |  | 10.38% |
Approved Equity Ratio |  |  |  |  |  |  |  | 54.29% |
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 |  |  |  |  |  | $ 23.1 | $ 25.1 | $ 71.7 | $ 73.9
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 |  |  |  | $ 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 |
Electric Rates [Member] | MPUC [Member] | 2016 Minnesota General Rate Case [Member] | Minnesota Power [Member] | Retail Customers [Member] | Boswell Energy Center [Member] |  |  |  |  |  |  |  |  |
Regulatory Matters [Line Items] |  |  |  |  |  |  |  |  |
Expected Decrease in Annual Depreciation Expense |  |  |  | $ 25.0 |  |  |  |  |
Electric Rates [Member] | MPUC [Member] | Renewable Cost Recovery Rider [Member] | Retail Customers [Member] | Corporate and Other [Member] |  |  |  |  |  |  |  |  |
Regulatory Matters [Line Items] |  |  |  |  |  |  |  |  |
After-Tax (Increase) Decrease for North Dakota Investment Tax Credits |  |  |  |  |  | (8.0) | 9.0 |  |
Electric Rates [Member] | MPUC [Member] | Renewable Cost Recovery Rider [Member] | Minnesota Power [Member] | Retail Customers [Member] | Sales [Member] |  |  |  |  |  |  |  |  |
Regulatory Matters [Line Items] |  |  |  |  |  |  |  |  |
Revenue Increase (Decrease) from Approved Rate |  |  |  |  |  | $ 14.0 | $ (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 |
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 December 2024) [Member] |  |  |  |  |  |  |  |  |
Regulatory Matters [Line Items] |  |  |  |  |  |  |  |  |
Number of Customers | Customers |  |  |  |  |  | 14 |  | 14 |
Electric Rates [Member] | FERC [Member] | FERC-Approved Wholesale Rates [Member] | Minnesota Power [Member] | Municipal Customers [Member] | Wholesale Electric Contracts (Expire December 2024) [Member] | Maximum [Member] |  |  |  |  |  |  |  |  |
Regulatory Matters [Line Items] |  |  |  |  |  |  |  |  |
Change in Annual Capacity Charge Per Contract, Percentage |  |  |  |  |  | 2.00% |  | 2.00% |
Electric Rates [Member] | FERC [Member] | FERC-Approved Wholesale Rates [Member] | Minnesota Power [Member] | Municipal Customers [Member] | Wholesale Electric Contracts (Expire December 2024) [Member] | Minimum [Member] |  |  |  |  |  |  |  |  |
Regulatory Matters [Line Items] |  |  |  |  |  |  |  |  |
Change in Annual Capacity Charge Per Contract, Percentage |  |  |  |  |  | (1.00%) |  | (1.00%) |
Electric Rates [Member] | PSCW [Member] | 2016 Wisconsin General Rate Case [Member] | SWL&P [Member] | Retail Customers [Member] |  |  |  |  |  |  |  |  |
Regulatory Matters [Line Items] |  |  |  |  |  |  |  |  |
Approved Rate Increase (Decrease) | 3.80% |  |  |  |  |  |  |  |
Natural Gas Rates [Member] | PSCW [Member] | 2016 Wisconsin General Rate Case [Member] | SWL&P [Member] | Retail Customers [Member] |  |  |  |  |  |  |  |  |
Regulatory Matters [Line Items] |  |  |  |  |  |  |  |  |
Approved Rate Increase (Decrease) | (4.80%) |  |  |  |  |  |  |  |
Water Rates [Member] | PSCW [Member] | 2016 Wisconsin General Rate Case [Member] | SWL&P [Member] | Retail Customers [Member] |  |  |  |  |  |  |  |  |
Regulatory Matters [Line Items] |  |  |  |  |  |  |  |  |
Approved Rate Increase (Decrease) | 9.80% |  |  |  |  |  |  |  |

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 The annual percentage change of the capacity charge specified in a power purchase, power sales, or electric sales agreement. + References No definition available. + Details
Name: | ale_ChangeinAnnualCapacityChargePerContractPercentage
Namespace Prefix: | ale_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | instant

X
- Definition Expected increase (decrease) in annual depreciation expense based on a regulatory order, if approved. + References No definition available. + Details
Name: | ale_ExpectedincreaseDecreaseinAnnualDepreciationExpenseBasedonaRegulatoryOrder
Namespace Prefix: | ale_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

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 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 rate increase (decrease) by regulatory agency. + References No definition available. + Details
Name: | us-gaap_PublicUtilitiesApprovedRateIncreaseDecreasePercentage
Namespace Prefix: | us-gaap_
Data Type: | num:percentItemType
Balance Type: | na
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
- Definition Amount of increase (decrease) to previously recorded tax expense. Includes, but is not limited to, significant settlements of income tax disputes, and unusual tax positions or infrequent actions taken by the entity, including tax assessment reversal, and IRS tax settlement. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 740 -SubTopic 10 -Section 25 -Paragraph 8 -URI http://asc.fasb.org/extlink&oid=96869850&loc=d3e28446-109314 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 740 -SubTopic 10 -Section 25 -Paragraph 10 -URI http://asc.fasb.org/extlink&oid=96869850&loc=d3e28511-109314 + Details
Name: | us-gaap_TaxAdjustmentsSettlementsAndUnusualProvisions
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

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: | ale_RateTypeAxis=ale_ElectricRatesMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

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

X
- Details
Name: | us-gaap_PublicUtilitiesRegulatoryProceedingAxis=ale_A2010RateCaseMember
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: | us-gaap_PublicUtilitiesRegulatoryProceedingAxis=ale_CurrentCostRecoveryRiderMember
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: | ale_GeneratingFacilityAxisAxis=ale_BoswellEnergyCenterMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

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

X
- Details
Name: | us-gaap_StatementBusinessSegmentsAxis=us-gaap_CorporateAndOtherMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_IncomeStatementLocationAxis=us-gaap_SalesMember
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_WholesaleElectricContractsExpireDecember2024Member
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_RangeAxis=us-gaap_MaximumMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_RangeAxis=us-gaap_MinimumMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

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

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