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Summary of Significant Accounting Policies Equity investment and excess costs (Details) - USD ($) $ in Millions | 12 Months Ended |
--- | --- | ---
Dec. 31, 2018 | Dec. 31, 2017
Schedule of Equity Method Investments [Line Items] |  |
Equity Method Investment, Difference Between Carrying Amount and Underlying Equity, Amortization Period | 12 years |
Amortized [Member] |  |
Schedule of Equity Method Investments [Line Items] |  |
Equity Method of Accounting and Excess Investment Cost | $ 470 | $ 732
Not Subject To Amortization But Subject to Impairment [Member] |  |
Schedule of Equity Method Investments [Line Items] |  |
Equity Method of Accounting and Excess Investment Cost | $ 1,967 | $ 1,967

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- Definition Difference between amount at which an investment accounted for under the equity method of accounting is carried (reported) on the balance sheet and amount of underlying equity in net assets the reporting Entity has in the investee. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 323 -SubTopic 10 -Section 50 -Paragraph 3 -Subparagraph (a)(3) -URI http://asc.fasb.org/extlink&oid=114001798&loc=d3e33918-111571 + Details
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