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Fair Value of Financial Instruments Financial Assets and Liabilities Recognized at Fair Value (Details) (USD $) | Sep. 30, 2012 | Dec. 31, 2011
--- | --- | ---
Estimate of Fair Value, Fair Value Disclosure [Member] |  |
Nuclear decommissioning trust (1): |  |
Money market funds | $ 14,000,000 | $ 14,000,000
Debt securities: |  |
Domestic | 15,000,000 | 12,000,000
Corporate credit | 8,000,000 | 11,000,000
Equity securities: |  |
Domestic | 5,000,000 | 9,000,000
International | 1,000,000 | 1,000,000
Debt securities - domestic government | 3,000,000 | 3,000,000
Assets from price risk management activities: |  |
Electricity | 2,000,000 | 2,000,000
Natural gas | 8,000,000 | 17,000,000
Total | 56,000,000 | 69,000,000
Liabilities from price risk management activities: |  |
Electricity | 96,000,000 | 137,000,000
Natural gas | 141,000,000 | 251,000,000
Total | 237,000,000 | 388,000,000
Fair Value, Inputs, Level 1 [Member] |  |
Nuclear decommissioning trust (1): |  |
Money market funds | 0 | 0
Debt securities: |  |
Domestic | 5,000,000 | 3,000,000
Corporate credit | 0 | 0
Equity securities: |  |
Domestic | 3,000,000 | 7,000,000
International | 1,000,000 | 1,000,000
Debt securities - domestic government | 3,000,000 | 3,000,000
Assets from price risk management activities: |  |
Electricity | 0 | 0
Natural gas | 0 | 0
Total | 12,000,000 | 14,000,000
Liabilities from price risk management activities: |  |
Electricity | 0 | 0
Natural gas | 0 | 0
Total | 0 | 0
Fair Value, Inputs, Level 2 [Member] |  |
Nuclear decommissioning trust (1): |  |
Money market funds | 14,000,000 | 14,000,000
Debt securities: |  |
Domestic | 10,000,000 | 9,000,000
Corporate credit | 8,000,000 | 11,000,000
Equity securities: |  |
Domestic | 2,000,000 | 2,000,000
International | 0 | 0
Debt securities - domestic government | 0 | 0
Assets from price risk management activities: |  |
Electricity | 1,000,000 | 2,000,000
Natural gas | 4,000,000 | 17,000,000
Total | 39,000,000 | 55,000,000
Liabilities from price risk management activities: |  |
Electricity | 63,000,000 | 108,000,000
Natural gas | 90,000,000 | 201,000,000
Total | 153,000,000 | 309,000,000
Fair Value, Inputs, Level 3 [Member] |  |
Nuclear decommissioning trust (1): |  |
Money market funds | 0 | 0
Debt securities: |  |
Domestic | 0 | 0
Corporate credit | 0 | 0
Equity securities: |  |
Domestic | 0 | 0
International | 0 | 0
Debt securities - domestic government | 0 | 0
Assets from price risk management activities: |  |
Electricity | 1,000,000 | 0
Natural gas | 4,000,000 | 0
Total | 5,000,000 | 0
Liabilities from price risk management activities: |  |
Electricity | 33,000,000 | 29,000,000
Natural gas | 51,000,000 | 50,000,000
Total | $ 84,000,000 | $ 79,000,000

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- Definition The aggregate fair value as of the balance sheet date of financial instruments and other positions owned by the entity including: (1) mortgages, mortgage-backed and asset backed securities; (2) US government and agency obligations; (3) state and municipal government obligations; (4) other sovereign government debt; (5) corporate obligations; (6) corporate equities; (7) principal investments; (8) derivative contracts; and (9) physical commodities. Includes both pledged and unpledged holdings. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 940 -SubTopic 320 -Section 45 -Paragraph 2 -URI http://asc.fasb.org/extlink&oid=6475986&loc=d3e42546-110969 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher AICPA -Name Audit and Accounting Guide (AAG) -Number AAG-BRD -Paragraph 38, 40 -IssueDate 2006-05-01 -Chapter 4 -LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy. Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher AICPA -Name Audit and Accounting Guide (AAG) -Number AAG-BRD -Paragraph 80 -Subparagraph Exhibit 4-3 -IssueDate 2006-05-01 -Chapter 4 -LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy. + Details
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- Definition This element represents the aggregate of the liabilities reported on the balance sheet at period end measured at fair value by the entity. This element is intended to be used in connection with the fair value disclosures required in the footnote disclosures to the financial statements. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 820 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=7578670&loc=d3e19207-110258 + Details
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- Definition Investment in short-term money-market instruments (such as commercial paper, banker's acceptances, repurchase agreements, government securities, certificates of deposit, and so forth) which are highly liquid (that is, readily convertible to known amounts of cash) and so near their maturity that they present an insignificant risk of changes in value because of changes in interest rates. Generally, only investments with original maturities of three months or less qualify as cash equivalents by definition. Original maturity means an original maturity to the entity holding the investment. For example, both a three-month US Treasury bill and a three-year Treasury note purchased three months from maturity qualify as cash equivalents. However, a Treasury note purchased three-years ago does not become a cash equivalent when its remaining maturity is three months. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Glossary Cash Equivalents -URI http://asc.fasb.org/extlink&oid=6507016 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 95 -Paragraph 8, 9 -LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy. + Details
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