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Quarterly Operating Results (Unaudited) - Realized gains, favorable (adverse) prior year development of the liability for losses and LAE and the impact of derivatives related to Fixed-indexed annuities (Details) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016
Realized gains (losses) and favorable (adverse) development on unpaid loss and loss adjustment expenses
Realized Gains (Losses) on Securities and Subsidiaries	$ 6	$ (12)	$ 8	$ 3	$ 51	$ 2	$ (14)	$ (18)	$ 5	$ 21
Prior Year Development Favorable (Adverse)	66	(52)	22	28	(10)	(22)	(28)	28	64	(32)
Impact of derivatives related to FIAs	$ (11)	$ (4)	$ (16)	$ (2)	$ 29	$ 1	$ (26)	$ (31)	$ (33)	$ (27)

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- Definition

Fixed-indexed annuities (FIAs) provide policyholders with a crediting rate tied, in part, to the performance of an existing stock market or other financial index. To mitigate the risk in the index-based component of these products, call options are purchased on the appropriate index. The change in the fair value of the call option assets will generally offset the economic change in the liabilities from the index participation. Both the index-based component of the annuities (an embedded derivative) and the related call options are considered derivatives that must be marked-to-market through earnings each period. Fluctuations in interest rates and the stock market, among other factors, can cause volatility in the periodic measurement of fair value of the embedded derivative. The net change in fair value of derivatives and the related impact of amortization of Deferred Policy Acquisition Costs are reflected in the impact of derivatives related to FIAs.

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- Definition

Realized gains (losses) on securities and subdiaries and favorable (unfavorable) development on unpaid loss and loss adjustment expenses.

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No definition available.

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- Definition

Realized gains losses on securities and subsidiaries.

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- Definition

Amount, after effects of reinsurance, of expense (reversal of expense) for claims incurred in prior reporting periods and related claims settlement costs.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 40
-Section 50
-Paragraph 3
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=65670824&loc=d3e14764-158437

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 235
-Section S99
-Paragraph 3
-Subparagraph (SX 210.12-18)
-URI http://asc.fasb.org/extlink&oid=34713774&loc=d3e575016-122915

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