Derivatives (Volumes Of Outstanding Derivative Contracts, In Megawatt Hours Unless Otherwise Specified) (Detail)	3 Months Ended		12 Months Ended
	Mar. 31, 2014		Dec. 31, 2013
Derivative [Line Items]
Derivatives expiration, lower (year)	2019 years		2019 years
Derivatives expiration, higher (year)	2023 years		2022 years
Forwards And Swaps [Member] | Natural Gas [Member]
Derivative [Line Items]
Less Than 1 Year	243,602,622	[1],[2],[3]	243,213,288	[1],[2],[3]
Greater Than 1 Year but Less Than 3 Years	76,235,312	[1],[2],[3]	79,735,000	[1],[2],[3]
Greater Than 3 Years but Less Than 5 Years	7,640,000	[1],[2],[3]	8,892,500	[1],[2],[3]
Greater Than 5 Years	0	[1],[2],[3],[4]	0	[1],[2],[3],[5]
Forwards And Swaps [Member] | Electricity [Member]
Derivative [Line Items]
Less Than 1 Year	2,132,784	[1]	2,537,023	[1]
Greater Than 1 Year but Less Than 3 Years	1,956,498	[1]	2,009,505	[1]
Greater Than 3 Years but Less Than 5 Years	1,871,208	[1]	2,008,046	[1]
Greater Than 5 Years	1,394,250	[1],[4]	1,534,695	[1],[5]
Options [Member] | Natural Gas [Member]
Derivative [Line Items]
Less Than 1 Year	140,209,906	[1],[2],[3]	169,123,208	[1],[2],[3]
Greater Than 1 Year but Less Than 3 Years	62,803,770	[1],[2],[3]	87,689,708	[1],[2],[3]
Greater Than 3 Years but Less Than 5 Years	2,550,000	[1],[2],[3]	3,450,000	[1],[2],[3]
Greater Than 5 Years	0	[1],[2],[3],[4]	0	[1],[2],[3],[5]
Congestion Revenue Rights [Member] | Electricity [Member]
Derivative [Line Items]
Less Than 1 Year	65,730,617	[1]	73,510,440	[1]
Greater Than 1 Year but Less Than 3 Years	83,761,019	[1]	83,747,782	[1]
Greater Than 3 Years but Less Than 5 Years	57,617,664	[1]	63,718,517	[1]
Greater Than 5 Years	27,407,793	[1],[4]	29,945,852	[1],[5]

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

[2] Million British Thermal Units.

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

[4] Derivatives in this category expire between 2019 and 2023.

[5] Derivatives in this category expire between 2019 and 2022.