Derivatives (Volumes Of Outstanding Derivative Contracts) (Detail)	1 Months Ended
	Jun. 30, 2012
Derivative [Line Items]
Derivatives expiration, lower (year)	2012 years
Derivatives expiration, higher (year)	2022 years
Forwards And Swaps [Member] | Natural Gas [Member]
Derivative [Line Items]
Less Than 1 Year	415,332,102	[1],[2]
Greater Than 1 Year but Less Than 3 Years	156,732,291	[1],[2]
Greater Than 3 Years but Less Than 5 Years	5,680,000	[1],[2]
Forwards And Swaps [Member] | Electricity [Member]
Derivative [Line Items]
Less Than 1 Year	5,010,023	[1]
Greater Than 1 Year but Less Than 3 Years	4,314,021	[1]
Greater Than 3 Years but Less Than 5 Years	2,009,505	[1]
Greater Than 5 Years	3,081,447	[1],[3]
Options [Member] | Natural Gas [Member]
Derivative [Line Items]
Less Than 1 Year	256,620,196	[1],[4]
Greater Than 1 Year but Less Than 3 Years	277,662,141	[1],[4]
Greater Than 3 Years but Less Than 5 Years	7,000,000	[1],[4]
Options [Member] | Electricity [Member]
Derivative [Line Items]
Greater Than 1 Year but Less Than 3 Years	174,559	[1]
Greater Than 3 Years but Less Than 5 Years	239,233	[1]
Greater Than 5 Years	183,964	[1],[3]
Congestion Revenue Rights [Member] | Electricity [Member]
Derivative [Line Items]
Less Than 1 Year	58,606,638	[1]
Greater Than 1 Year but Less Than 3 Years	73,139,741	[1]
Greater Than 3 Years but Less Than 5 Years	73,207,008	[1]
Greater Than 5 Years	44,412,837	[1],[3]

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

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

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

[4] Million British Thermal Units.