Derivative Financial Instruments (Open Gross Derivative Volumes By Commodity Type) (Details)	Dec. 31, 2011		Dec. 31, 2010
Coal (In Tons) [Member]
Derivative [Line Items]
NPNS Contract	147,000,000	[1]	73,000,000	[1]
Fuel Oils (In Gallons) [Member]
Derivative [Line Items]
Other Derivatives	36,000,000	[2],[3]	55,000,000	[3]
Derivatives That Qualify for Regulatory Deferral	53,000,000	[4]	80,000,000	[4]
Natural Gas (In Mmbtu) [Member]
Derivative [Line Items]
NPNS Contract	50,000,000	[1]	98,000,000	[1]
Other Derivatives	17,000,000	[2],[3]	21,000,000	[3]
Derivatives That Qualify for Regulatory Deferral	193,000,000	[4]	194,000,000	[4]
Power (In Megawatt Hours) [Member]
Derivative [Line Items]
NPNS Contract	73,000,000	[1]	63,000,000	[1]
Cash Flow Hedges	17,000,000	[2],[3]	2,000,000	[2],[3]
Other Derivatives	31,000,000	[2],[3]	61,000,000	[3]
Derivatives That Qualify for Regulatory Deferral	21,000,000	[4]	18,000,000	[4]
Uranium (In Pounds) [Member]
Derivative [Line Items]
NPNS Contract	5,553,000	[1]	5,810,000	[1]
Derivatives That Qualify for Regulatory Deferral	148,000	[4]	185,000	[4]

[1] Contracts through December 2017, March 2015, September 2035, and October 2024 for coal, natural gas, power, and uranium, respectively, as of December 31, 2011.

[2] Contracts through December 2014 for power as of December 31, 2011.

[3] Contracts through October 2014, December 2012, and December 2015 for fuel oils, natural gas, and power, respectively, as of December 31, 2011.

[4] Contracts through October 2014, October 2016, May 2032, and December 2013 for fuel oils, natural gas, power, and uranium, respectively, as of December 31, 2011.