Investments (Net realized investment gains (losses)) (Details) - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Net realized investment gains (losses)	$ 50	$ (67)	$ 57
Fixed maturity securities [Member]
Gross realized gains	204	131	170
Gross realized losses	(138)	(197)	(129)
Net realized investment gains (losses)	66	(66)	41
Total equity securities available-for-sale [Member]
Gross realized gains	5	2	8
Gross realized losses	(10)	(25)	(7)
Net realized investment gains (losses)	(5)	(23)	1
Derivative [Member]
Net realized investment gains (losses)	(2)	10	(1)
Short term investments and other [Member]
Net realized investment gains (losses)	$ (9)	$ 12	$ 16

This item represents the difference between the gross realized gains and losses realized on the sale of debt or equity securities categorized neither as held-to-maturity nor trading securities. Additionally, this item would include any losses recognized for other than temporary impairments (OTTI) of the subject investments in debt and equity securities.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 9
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=73527792&loc=d3e27357-111563

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