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Regulatory Matters - Great Northern Transmission Line (GNTL) (Details) (Great Northern Transmission Line [Member])	Mar. 31, 2014 kV Miles
Great Northern Transmission Line [Member]
Transmission [Line Items]
Transmission Line Length (Miles)	220
Transmission Line Capacity (kV)	500

X

- Definition

Capacity of a transmission line in kilovolts.

+ References

No definition available.

+ Details

Name:	ale_TransmissionLineCapacityKv
Namespace Prefix:	ale_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	instant

X

- Details

Name:	ale_TransmissionLineItems
Namespace Prefix:	ale_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

X

- Definition

Length of a transmission line in miles.

+ References

No definition available.

+ Details

Name:	ale_TransmissionLineLengthMiles
Namespace Prefix:	ale_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	instant