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Investments Schedule of Gains and Losses on Equity and Other Investments (Details) - USD ($) $ in Millions | 12 Months Ended
--- | ---
Dec. 31, 2018 | Dec. 31, 2017 | Dec. 31, 2016
Gain (Loss) on Securities [Line Items] |  |  |
Unrealized Gain (Loss) on Investments | $ (1,699) | $ 392 | $ 184
Equity Securities [Member] |  |  |
Gain (Loss) on Securities [Line Items] |  |  |
Equity Securities, FV-NI, Realized Gain (Loss) | (59) |  |
Unrealized Gain (Loss) on Investments | 0 | 88 | 52
Other Investments [Member] |  |  |
Gain (Loss) on Securities [Line Items] |  |  |
Realized Investment Gains (Losses) | (5) | $ 0 | $ 0
Accounting Standards Update 2016-01 [Member] | Equity Securities [Member] |  |  |
Gain (Loss) on Securities [Line Items] |  |  |
Equity Securities, FV-NI, Realized Gain (Loss) | (59) |  |
Unrealized Gain (Loss) on Investments | (129) |  |
Gain (Loss) on Sale of Investments | 70 |  |
Accounting Standards Update 2016-01 [Member] | Other Investments [Member] |  |  |
Gain (Loss) on Securities [Line Items] |  |  |
Unrealized Gain (Loss) on Investments | (126) |  |
Gain (Loss) on Sale of Investments | 121 |  |
Realized Investment Gains (Losses) | (5) |  |
Accounting Standards Update 2016-01 [Member] | Equity securities and other investments [Member] |  |  |
Gain (Loss) on Securities [Line Items] |  |  |
Unrealized Gain (Loss) on Investments | (255) |  |
Gain (Loss) on Sale of Investments | 191 |  |
Realized Investment Gains (Losses) | $ (64) |  |

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- Definition Amount of realized gain (loss) from sale of investment in equity security measured at fair value with change in fair value recognized in net income (FV-NI). + References Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef -Publisher FASB -Name Accounting Standards Codification -Topic 321 -SubTopic 10 -Section 50 -Paragraph 4 -URI http://asc.fasb.org/extlink&oid=84241550&loc=SL75117546-209714 + Details
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- Definition The net realized gain (loss) on investments sold during the period, not including gains (losses) on securities separately or otherwise categorized as trading, available-for-sale, or held-to-maturity, which, for cash flow reporting, is a component of proceeds from investing activities. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 230 -SubTopic 10 -Section 45 -Paragraph 28 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=109223946&loc=d3e3602-108585 + Details
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- Definition The net realized gains or losses on investments during the period, not including gains or losses on securities separately or otherwise categorized as trading, available-for-sale, or held-to-maturity. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 944 -SubTopic 220 -Section S99 -Paragraph 1 -Subparagraph (SX 210.7-04.3(a)) -URI http://asc.fasb.org/extlink&oid=114873790&loc=SL114874131-224263 + Details
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- Definition The net change in the difference between the fair value and the carrying value, or in the comparative fair values, of investments, not including unrealized gains or losses on securities separately or otherwise categorized as trading, available-for-sale, or held-to-maturity, held at each balance sheet date and included in earnings for the period. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 230 -SubTopic 10 -Section 45 -Paragraph 28 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=109223946&loc=d3e3602-108585 + Details
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