Commitments, Guarantees and Contingencies - Transmission (Details) (USD $) In Millions, unless otherwise specified	Sep. 30, 2011
Transmission [Line Items]
MPUC, Billing Factor, Approval Date	May 11, 2011
MPUC, Updated Billing Factor, Filing Date	Jun. 29, 2011
MPUC, Updated Billing Factor, Expected Approval Date	2011
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	$ 19.7
CapX2020 Fargo to St. Cloud Project [Member]
Transmission [Line Items]
MPUC, Route Permit, Approval Date	Jun. 10, 2011
CapX2020 Monticello to St. Cloud Project [Member]
Transmission [Line Items]
Transmission Line Length (Miles)	28
Transmission Line Capacity (kV)	345
MPUC, Route Permit, Approval Date	July 2010
Project Completion Date	2011
CapX2020 Bemidji to Grand Rapids Project [Member]
Transmission [Line Items]
Transmission Line Length (Miles)	70
Transmission Line Capacity (kV)	230
CapX2020 Fargo to Monticello Projects [Member]
Transmission [Line Items]
Transmission Line Length (Miles)	238
Transmission Line Capacity (kV)	345
In Service Date	2015