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Other Investments (Amortized Cost and Fair Value of Nuclear Decommissioning Trusts) (Details) (USD $) | 3 Months Ended | 6 Months Ended | 12 Months Ended |  |  |
--- | --- | --- | --- | --- | --- | ---
Jun. 30, 2012 | Jun. 30, 2011 | Jun. 30, 2012 | Jun. 30, 2011 | Dec. 31, 2011 | Mar. 31, 2012 | Mar. 31, 2011 | Dec. 31, 2010
Fair Value Disclosures: |  |  |  |  |  |  |  |
Contributions received for decommissioning trusts |  |  | $ 23,000,000 |  |  |  |  |
Period of reviewing contributions from decommissioning trusts (in years) |  |  | 3 years |  |  |  |  |
Nuclear Decommissioning Trusts Disclosures |  |  |  |  |  |  |  |
Amortized Cost | 2,406,000,000 |  | 2,406,000,000 |  | 2,303,000,000 |  |  |
Fair Value | 3,810,000,000 | 3,657,000,000 | 3,810,000,000 | 3,657,000,000 | 3,592,000,000 | 3,853,000,000 | 3,619,000,000 | 3,480,000,000
Proceeds from sale of securities | 496,000,000 | 524,000,000 | 1,097,000,000 | 1,146,000,000 |  |  |  |
Unrealized holding gains, net of losses |  |  | 1,400,000,000 |  | 1,300,000,000 |  |  |
Stocks |  |  |  |  |  |  |  |
Nuclear Decommissioning Trusts Disclosures |  |  |  |  |  |  |  |
Amortized Cost | 953,000,000 |  | 953,000,000 |  | 865,000,000 |  |  |
Fair Value | 2,090,000,000 |  | 2,090,000,000 |  | 1,899,000,000 |  |  |
Municipal bonds |  |  |  |  |  |  |  |
Nuclear Decommissioning Trusts Disclosures |  |  |  |  |  |  |  |
Longest maturity dates decommissioning trust investments (in years) |  |  | 2051 |  |  |  |  |
Amortized Cost | 583,000,000 |  | 583,000,000 |  | 625,000,000 |  |  |
Fair Value | 714,000,000 |  | 714,000,000 |  | 756,000,000 |  |  |
U.S. government and agency securities |  |  |  |  |  |  |  |
Nuclear Decommissioning Trusts Disclosures |  |  |  |  |  |  |  |
Longest maturity dates decommissioning trust investments (in years) |  |  | 2041 |  |  |  |  |
Amortized Cost | 489,000,000 |  | 489,000,000 |  | 516,000,000 |  |  |
Fair Value | 549,000,000 |  | 549,000,000 |  | 580,000,000 |  |  |
Corporate bonds |  |  |  |  |  |  |  |
Nuclear Decommissioning Trusts Disclosures |  |  |  |  |  |  |  |
Longest maturity dates decommissioning trust investments (in years) |  |  | 2054 |  |  |  |  |
Amortized Cost | 310,000,000 |  | 310,000,000 |  | 259,000,000 |  |  |
Fair Value | 382,000,000 |  | 382,000,000 |  | 317,000,000 |  |  |
Short-term investments and receivables/payables |  |  |  |  |  |  |  |
Nuclear Decommissioning Trusts Disclosures |  |  |  |  |  |  |  |
Longest maturity dates decommissioning trust investments (in years) |  |  | One-year |  |  |  |  |
Amortized Cost | 71,000,000 |  | 71,000,000 |  | 38,000,000 |  |  |
Fair Value | $ 75,000,000 |  | $ 75,000,000 |  | $ 40,000,000 |  |  |

X
- Definition The amount of decommissioning trust assets at amortized cost as of the balance sheet date. + References No definition available. + Details
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- Definition Amount of contributions from customers into the decommissioning trusts. + References No definition available. + Details
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- Definition The maturity dates for decommissioning trust investments. + References No definition available. + Details
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- Definition The period of reviewing and revising contributions from decommissioning trusts. + References No definition available. + Details
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- Definition This item represents the difference between the gross realized gains and losses realized on the sale of debt or equity securities categorized neither as held-to-maturity nor trading securities. Additionally, this item would include any losses recognized for other than temporary impairments (OTTI) of the subject investments in debt and equity securities. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 115 -Paragraph 16 -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 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 50 -Paragraph 9 -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=6872113&loc=d3e27357-111563 + Details
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- Definition The fair value of investments held in a trust fund to pay for the costs of decontaminating and decommissioning facilities, whether such amount is presented as a separate caption or as a parenthetical disclosure on the balance sheet. Additionally, this element may 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 Statement of Financial Accounting Standard (FAS) -Number 143 -Paragraph 22 -Subparagraph b -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 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 410 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=6392692&loc=d3e7535-110849 + Details
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- Definition The cash inflow from the sale of assets held in a decommissioning trust fund. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 230 -SubTopic 10 -Section 45 -Paragraph 12 -URI http://asc.fasb.org/extlink&oid=6943989&loc=d3e3179-108585 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Glossary Investing Activities -URI http://asc.fasb.org/extlink&oid=6516133 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 95 -Paragraph 15, 16 -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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