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Fair Value Measurements (Details 3) - USD ($) $ in Millions | Dec. 31, 2016 | Dec. 31, 2015
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Debt securities |  |
Amortized cost basis, unrealized gains and losses and fair values of investments in available-for-sale securities |  |
Cost Basis | $ 1,735 | $ 1,778
Unrealized Gains | 38 | 16
Fair Value | 1,773 | 1,794
Equity securities |  |
Amortized cost basis, unrealized gains and losses and fair values of investments in available-for-sale securities |  |
Cost Basis | 822 | 542
Unrealized Gains | 103 | 34
Fair Value | 925 | 576
FES | Debt securities |  |
Amortized cost basis, unrealized gains and losses and fair values of investments in available-for-sale securities |  |
Cost Basis | 847 | 801
Unrealized Gains | 27 | 9
Fair Value | 874 | 810
FES | Equity securities |  |
Amortized cost basis, unrealized gains and losses and fair values of investments in available-for-sale securities |  |
Cost Basis | 564 | 354
Unrealized Gains | 70 | 24
Fair Value | $ 634 | $ 378

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- Definition Amount of investment in debt and equity securities categorized neither as held-to-maturity nor trading. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 25 -Paragraph 1 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=65884222&loc=d3e22054-111558 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 50 -Paragraph 5 -Subparagraph (aa) -URI http://asc.fasb.org/extlink&oid=73527792&loc=d3e27232-111563 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=66010992&loc=d3e26610-111562 + Details
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- Definition Amount before tax of unrealized gain in accumulated other comprehensive income (AOCI) on investments in debt and equity securities classified as available-for-sale. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=73527792&loc=d3e27161-111563 + Details
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- Definition This item represents the cost of debt and equity securities, which are categorized neither as held-to-maturity nor trading, net of adjustments including accretion, amortization, collection of cash, previous other-than-temporary impairments recognized in earnings (less any cumulative-effect adjustments recognized, as defined), and fair value hedge accounting adjustments, if any. + 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 210.5-02.2) -URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682 + Details
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