XML 53 R40.htm IDEA: XBRL DOCUMENT
v3.7.0.1

Operations and Significant Accounting Policies - Reclassification of Prior Income Statement (Details) - USD ($) $ in Millions | 3 Months Ended | 6 Months Ended
--- | --- | ---
Jun. 30, 2016 | Jun. 30, 2016
Operating Revenue to Operating Revenue – Utility [Member] |  |
Reclassification of Prior Income Statement [Line Items] |  |
Prior Period Reclassification Amount | $ 234.9 | $ 487.2
Operating Revenue to Operating Revenue – Non-utility [Member] |  |
Reclassification of Prior Income Statement [Line Items] |  |
Prior Period Reclassification Amount | 79.9 | 161.4
Cost of Sales – Non-utility to Fuel, Purchased Power and Gas – Utility [Member] |  |
Reclassification of Prior Income Statement [Line Items] |  |
Prior Period Reclassification Amount | $ 0.9 | $ 3.9

X
- Definition [Line Items] for Schedule of prior period reclassification adjustments to conform the presentation of prior period financial statements with the presentation in the current period. + References No definition available. + Details
Name: | ale_ScheduleofPriorPeriodReclassificationAdjustmentsLineItems
Namespace Prefix: | ale_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

X
- Definition The amount of a reclassification adjustment made to prior period financial statement amounts. + References No definition available. + Details
Name: | us-gaap_PriorPeriodReclassificationAdjustment
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

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

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

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