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Fair Value Measurements Investments Gains (Losses) (Details) - USD ($) $ in Millions | 3 Months Ended
--- | ---
Dec. 31, 2015 | Dec. 31, 2014
Investment Gains (Losses) |  |
Securities classified as trading and measured at fair value | $ 2,100 |
NDT unfunded commitments related to private partnerships | 79 |
Nuclear Decommissioning Fund Investments, Fair Value | 1,500 |
Decommissioning Fund Investments, Fair Value | 449 |
SERP |  |
Investment Gains (Losses) |  |
Unrealized gains (losses) on investments | 0 | $ (1)
LTDCP |  |
Investment Gains (Losses) |  |
Unrealized gains (losses) on investments | 0 | (1)
NDT |  |
Investment Gains (Losses) |  |
Unrealized gains (losses) on investments | 39 | 23
ART |  |
Investment Gains (Losses) |  |
Unrealized gains (losses) on investments | 12 | $ 6
Maximum |  |
Investment Gains (Losses) |  |
Derivative Credit Risk Valuation Adjustment, Derivative Assets | 1 |
Equity investments not required to be measured at fair value | $ 1 |

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- Definition Fair value portion of arrangements with third parties, including, but not limited to, operating lease arrangement and arrangement in which the entity has agreed to expend funds to procure goods or services, or has agreed to commit resources to supply goods or services. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02.25) -URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 03 -Paragraph 19 -Article 7 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 03 -Paragraph 17 -Article 9 + Details
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- Definition This item represents the carrying amount on the entity's balance sheet of its investment in common stock of an equity method investee. This is not an indicator of the fair value of the investment, rather it is the initial cost adjusted for the entity's share of earnings and losses of the investee, adjusted for any distributions (dividends) and other than temporary impairment (OTTI) losses recognized. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 323 -SubTopic 10 -Section 45 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=35755396&loc=d3e33749-111570 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02.12) -URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682 + Details
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- Definition Amount of investments in debt and equity securities and other forms of securities that provide ownership interests classified as trading. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 45 -Paragraph 2 -URI http://asc.fasb.org/extlink&oid=49167202&loc=d3e26626-111562 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 942 -SubTopic 210 -Section S99 -Paragraph 1 -Subparagraph (SX 210.9-03.4) -URI http://asc.fasb.org/extlink&oid=6876686&loc=d3e534808-122878 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 45 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=49167202&loc=d3e26610-111562 Reference 4: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Glossary Trading Securities -URI http://asc.fasb.org/extlink&oid=6526789 + Details
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