Derivative Financial Instruments (Open Gross Derivative Volumes by Commodity Type) (Details)	Jun. 30, 2011		Dec. 31, 2010
Coal (in tons) [Member]
NPNS Contract	66,000,000	[1]	73,000,000	[1]
Heating Oil (in gallons) [Member]
Other Derivatives	40,000,000	[2]	55,000,000	[2]
Derivatives That Qualify for Regulatory Deferral	62,000,000	[3]	80,000,000	[3]
Natural Gas (in mmbtu) [Member]
NPNS Contract	72,000,000	[1]	98,000,000	[1]
Other Derivatives	26,000,000	[2]	21,000,000	[2]
Derivatives That Qualify for Regulatory Deferral	196,000,000	[3]	194,000,000	[3]
Power (in Megawatt Hours) [Member]
NPNS Contract	79,000,000	[1]	63,000,000	[1]
Cash Flow Hedges	21,000,000	[4]	2,000,000	[4]
Other Derivatives	54,000,000	[2]	61,000,000	[2]
Derivatives That Qualify for Regulatory Deferral	20,000,000	[3]	18,000,000	[3]
Uranium (in pounds) [Member]
NPNS Contract	5,710,000	[1]	5,810,000	[1]
Derivatives That Qualify for Regulatory Deferral	458,000	[3]	185,000	[3]

[1] Contracts through December 2014, March 2015, September 2035, and October 2024 for coal, natural gas, power, and uranium, respectively, as of June 30, 2011.

[2] Contracts through December 2013, December 2012, and May 2015 for heating oil, natural gas, and power, respectively, as of June 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 June 30, 2011.

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