Basis of Presentation and Significant Accounting Policies FX gain (loss) (Details) - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Foreign Currency Transaction Gain (Loss), before Tax	$ 12	$ (7)	$ 21
Premiums Receivable [Member]
Foreign Currency Transaction Gain (Loss), before Tax	(10)	2	(2)
Lossandlossreserves [Member]
Foreign Currency Transaction Gain (Loss), before Tax	(1)	(15)	29
Gain (Loss) on Investments [Member]
Foreign Currency Transaction Gain (Loss), before Tax	$ 22	$ 7	$ (5)

Amount before tax of foreign currency transaction realized and unrealized gain (loss) recognized in the income statement.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
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Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
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Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
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-Name Accounting Standards Codification
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