Commitments and Contingent Liabilities, Capital Commitments (Details) (Capital Commitments [Member])	Dec. 31, 2011 MW
Monticello and Prairie Island Nuclear Plants [Member]
Capital Commitments [Abstract]
Capacity increases (in MW)	188
CapX2020 [Member]
Capital Commitments [Abstract]
Number of transmission lines in Group 1 project	4
Clean Air Clean Jobs Act [Member]
Capital Commitments [Abstract]
Percentage reduction in annual emissions of NOx from 2008 levels, lower range	70.00%
Percentage reduction in annual emissions of NOx from 2008 levels, higher range	80.00%