Summary Of Significant Accounting Policies (Significant Unobservable Inputs in Asset Valuation) (Details) (Vermont Yankee [Member])	Jul. 31, 2013	Mar. 31, 2012
Weighted average cost of capital, Weighted Average	7.50%	7.80%
Long-term pre-tax operating margin (cash basis), Weighted Average	7.00%	7.20%
Minimum [Member]
Weighted average cost of capital, Range		7.50%
Long-term pre-tax operating margin (cash basis), Range		6.10%
Maximum [Member]
Weighted average cost of capital, Range		8.00%
Long-term pre-tax operating margin (cash basis), Range		7.80%