Derivatives (Volumes Of Outstanding Derivative Contracts) (Details)	Mar. 31, 2012
Derivative [Line Items]
Derivatives expiration, lower (year)	2017
Derivatives expiration, higher (year)	2022
Forwards And Swaps [Member] | Natural Gas [Member]
Derivative [Line Items]
Less Than 1 Year	439,441,427	[1],[2],[3]
Greater Than 1 Year but Less Than 3 Years	166,878,481	[1],[2],[3]
Greater Than 3 Years but Less Than 5 Years	4,280,000	[1],[2],[3]
Forwards And Swaps [Member] | Electricity [Member]
Derivative [Line Items]
Less Than 1 Year	4,141,223	[1]
Greater Than 1 Year but Less Than 3 Years	4,696,221	[1]
Greater Than 3 Years but Less Than 5 Years	2,009,505	[1]
Greater Than 5 Years	3,421,832	[1],[4]
Options [Member] | Natural Gas [Member]
Derivative [Line Items]
Less Than 1 Year	231,380,020	[1]
Greater Than 1 Year but Less Than 3 Years	280,200,000	[1]
Options [Member] | Electricity [Member]
Derivative [Line Items]
Less Than 1 Year	1,248,000	[1]
Greater Than 1 Year but Less Than 3 Years	140,510	[1]
Greater Than 3 Years but Less Than 5 Years	239,233	[1]
Greater Than 5 Years	218,013	[1],[4]
Congestion Revenue Rights [Member] | Electricity [Member]
Derivative [Line Items]
Less Than 1 Year	75,532,338	[1]
Greater Than 1 Year but Less Than 3 Years	73,123,024	[1]
Greater Than 3 Years but Less Than 5 Years	73,190,271	[1]
Greater Than 5 Years	54,209,541	[1],[4]

[1] Amounts shown reflect the total gross derivative volumes by commodity type that are expected to settle in each time period.

[2] Amounts shown are for the combined positions of the electric fuels and core gas portfolios.

[3] Million British Thermal Units.

[4] Derivatives in this category expire between 2017 and 2022.