Derivative Financial Instruments (Open Gross Derivative Volumes By Commodity Type) (Details)	Sep. 30, 2011	Dec. 31, 2010
Coal (In Tons) [Member]
Derivative [Line Items]
NPNS Contract	157,000,000	73,000,000	[1]
Heating Oil (In Gallons) [Member]
Derivative [Line Items]
Other Derivatives	43,000,000	55,000,000	[2]
Derivatives That Qualify for Regulatory Deferral	62,000,000	80,000,000	[3]
Natural Gas (In Mmbtu) [Member]
Derivative [Line Items]
NPNS Contract	60,000,000	98,000,000	[1]
Other Derivatives	26,000,000	21,000,000	[2]
Derivatives That Qualify for Regulatory Deferral	207,000,000	194,000,000	[3]
Power (In Megawatt Hours) [Member]
Derivative [Line Items]
NPNS Contract	73,000,000	63,000,000	[1]
Cash Flow Hedges	17,000,000	2,000,000	[4]
Other Derivatives	32,000,000	61,000,000	[2]
Derivatives That Qualify for Regulatory Deferral	21,000,000	18,000,000	[3]
Uranium (In Pounds) [Member]
Derivative [Line Items]
NPNS Contract	5,710,000	5,810,000	[1]
Derivatives That Qualify for Regulatory Deferral	308,000	185,000	[3]

[1] Contracts through December 2017, March 2015, September 2035, and October 2024 for coal, natural gas, power, and uranium, respectively, as of September 30, 2011.

[2] Contracts through October 2014, December 2012, and April 2015 for heating oil, natural gas, and power, respectively, as of September 30, 2011.

[3] Contracts through December 2013, October 2016, May 2032 and December 2013 for heating oil, natural gas, power, and uranium, respectively, as of September 30, 2011.

[4] Contracts through December 2013 for power as of September 30, 2011.