Derivatives And Hedging Activities (Volumes Of Outstanding Derivative Contracts) (Details)	Sep. 30, 2011
Derivative [Line Items]
Derivatives expiration, lower	2016
Derivatives expiration, higher	2022
Forwards And Futures Swaps [Member] | Natural Gas [Member]
Derivative [Line Items]
Less Than 1 Year	520,257,890	[1],[2],[3]
Greater Than 1 Year but Less Than 3 Years	247,388,834	[1],[2],[3]
Greater Than 3 Years but Less Than 5 Years	9,990,000	[1],[2],[3]
Forwards And Futures Swaps [Member] | Electricity [Member]
Derivative [Line Items]
Less Than 1 Year	4,703,003	[2]
Greater Than 1 Year but Less Than 3 Years	5,648,312	[2]
Greater Than 3 Years but Less Than 5 Years	2,528,599	[2]
Greater Than 5 Years	3,903,048	[2],[4]
Options [Member] | Natural Gas [Member]
Derivative [Line Items]
Less Than 1 Year	251,652,959	[2]
Greater Than 1 Year but Less Than 3 Years	313,795,682	[2]
Greater Than 3 Years but Less Than 5 Years	23,700,000	[2]
Options [Member] | Electricity [Member]
Derivative [Line Items]
Less Than 1 Year	2,074	[2]
Greater Than 1 Year but Less Than 3 Years	106,980	[2]
Greater Than 3 Years but Less Than 5 Years	264,348	[2]
Greater Than 5 Years	289,164	[2],[4]
Congestion Revenue Rights [Member] | Electricity [Member]
Derivative [Line Items]
Less Than 1 Year	49,296,971	[2]
Greater Than 1 Year but Less Than 3 Years	72,732,318	[2]
Greater Than 3 Years but Less Than 5 Years	72,771,156	[2]
Greater Than 5 Years	69,900,050	[2],[4]

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

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

[3] Million British Thermal Units.

[4] Derivatives in this category expire between 2016 and 2022.