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Commitments, Guarantees and Contingencies - Transmission (Details) (USD $) In Millions, unless otherwise specified	Dec. 31, 2011
Transmission [Line Items]
MPUC, Billing Factor, Approval Date	May 2011
MPUC, Updated Billing Factor, Filing Date	June 29, 2011
MPUC, Updated Billing Factor, Expected Approval Date	2012
CapX2020 Bemidji to Grand Rapids Project [Member]
Transmission [Line Items]
Transmission Line Length (Miles)	70
Transmission Line Capacity (kV)	230
CapX2020 Monticello to St. Cloud Project [Member]
Transmission [Line Items]
Transmission Line Length (Miles)	28
Transmission Line Capacity (kV)	345
Project Completion Date	December 2011
MPUC, Route Permit, Approval Date	July 2010
CapX2020 Fargo to St. Cloud Project [Member]
Transmission [Line Items]
MPUC, Route Permit, Approval Date	June 10, 2011
CapX2020 Fargo to Monticello Projects [Member]
Transmission [Line Items]
Transmission Line Length (Miles)	238
Transmission Line Capacity (kV)	345
Projected In Service Date	2015
CapX2020 [Member]
Transmission [Line Items]
Number of Projects	3
Minimum Amount Expected to be Invested in Transmission Projects	100
Maximum Amount Expected to be Invested in Transmission Projects	125
Capital Cost Spent to Date	27.8

X

- Definition

Capital cost spent to date for project.

+ References

No definition available.

+ Details

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X

- Definition

Date/expected date an asset will be in service.

+ References

No definition available.

+ Details

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X

- Definition

The maximum amount expected to be invested in transmission line projects.

+ References

No definition available.

+ Details

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X

- Definition

The minimum amount expected to be invested in transmission line projects.

+ References

No definition available.

+ Details

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X

- Definition

Date/expected date of approval by the Minnesota Public Utilities Commission (MPUC) of billing factor.

+ References

No definition available.

+ Details

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X

- Definition

Date/expected date of approval by the Minnesota Public Utilities Commission (MPUC) of route permit.

+ References

No definition available.

+ Details

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X

- Definition

Date/expected date of approval by the Minnesota Public Utilities Commission of updated billing factor.

+ References

No definition available.

+ Details

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Namespace Prefix:	ale_
Data Type:	us-types:dateStringItemType
Balance Type:	na
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X

- Definition

Filing date of petition to the Minnesota Public Utilities Commission (MPUC) seeking updated billing factor approval.

+ References

No definition available.

+ Details

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X

- Definition

Number of projects.

+ References

No definition available.

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- Definition

Date/expected date of project completion.

+ References

No definition available.

+ Details

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X

- Definition

Capacity of a transmission line in kilovolts.

+ References

No definition available.

+ Details

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- Details

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- Definition

Length of a transmission line in miles.

+ References

No definition available.

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