XML 78 R59.htm IDEA: XBRL DOCUMENT v3.8.0.1

Regulatory Matters - Conservation Improvement Program (CIP) (Details) - MPUC [Member] - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Minimum [Member]
Regulatory Matters [Line Items]
CIP Spending Minimum - Percentage	1.50%
CIP Triennial Filing [Member] | Minnesota Power [Member]
Regulatory Matters [Line Items]
CIP Annual Energy-Savings Goal - Percentage	1.50%
CIP Investment Goal	$ 10.3	$ 7.3	$ 7.1
CIP Actual Spending	8.1	7.4	6.6
CIP Investment Goal in 2018	10.3
CIP Investment Goal in 2019	10.5
CIP Consolidated Filing [Member] | Minnesota Power [Member]
Regulatory Matters [Line Items]
CIP Financial Incentive	$ 5.5	$ 7.5	$ 6.2

X

- Definition

Conservation improvement program actual annual spend.

+ References

No definition available.

+ Details

Name:	ale_CIPActualSpend
Namespace Prefix:	ale_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

X

- Definition

Minnesota's Next Generation Act of 2007 introduced an energy-savings goal of 1.5 percent of net gross annual retail electric energy sales beginning with the 2010 program year.

+ References

No definition available.

+ Details

Name:	ale_CIPEnergySavingsGoal
Namespace Prefix:	ale_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

X

- Definition

Conservation improvement program Investment Goal approved by MPUC.

+ References

No definition available.

+ Details

Name:	ale_CIPInvestmentGoal
Namespace Prefix:	ale_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

X

- Definition

Conservation improvement program Investment Goal for year three approved by the MPUC.

+ References

No definition available.

+ Details

Name:	ale_CIPInvestmentGoalYearThree
Namespace Prefix:	ale_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

X

- Definition

Conservation improvement program Investment Goal for year two approved by the MPUC.

+ References

No definition available.

+ Details

Name:	ale_CIPInvestmentGoalYearTwo
Namespace Prefix:	ale_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

X

- Definition

Minnesota's Next Generation Act of 2007 introduced a spend goal of 1.5% of net gross operating revenues from service provided in the state on energy CIPs each year.

+ References

No definition available.

+ Details

Name:	ale_CIPSpendRequirement
Namespace Prefix:	ale_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

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

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_RangeAxis=us-gaap_MinimumMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

Name:	us-gaap_PublicUtilitiesRegulatoryProceedingAxis=ale_CIPTriennialFilingMember
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_CIPAnnualFilingMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: