Investments (Net investment income) (Details) - USD ($) $ in Millions	3 Months Ended	9 Months Ended
Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Net Investment Income [Line Items]
Gross investment income	$ 538	$ 371	$ 1,504	$ 1,458
Investment expense	(14)	(17)	(43)	(46)
Net investment income	524	354	1,461	1,412
Fixed maturity securities [Member]
Net Investment Income [Line Items]
Gross investment income	457	449	1,352	1,344
Total equity securities available-for-sale [Member]
Net Investment Income [Line Items]
Gross investment income	1	3	8	9
Limited partnership investments [Member]
Net Investment Income [Line Items]
Gross investment income	65	(93)	97	69
Mortgage loans [Member]
Net Investment Income [Line Items]
Gross investment income	8	8	30	25
Short term investments [Member]
Net Investment Income [Line Items]
Gross investment income	2	2	6	4
Trading portfolio [Member]
Net Investment Income [Line Items]
Gross investment income	1	1	7	6
Other Investment Income [Member]
Net Investment Income [Line Items]
Gross investment income	$ 4	$ 1	$ 4	$ 1

Investment Income Including Realized Gains Losses on Trading Securities, Before Expenses

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- Definition

Investment income derived from investments in debt and equity securities consisting of interest income earned from investments in debt securities and on cash and cash equivalents, dividend income from investments in equity securities and income or expense derived from the amortization of investment related discounts or premiums, respectively. It also includes realized gains (losses) on trading securities.

+ References

No definition available.

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- Definition

Amount of expenses related to the generation of investment income.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 225
-SubTopic 10
-Section S99
-Paragraph 2
-Subparagraph (SX 210.5-03.9)
-URI http://asc.fasb.org/extlink&oid=26872669&loc=d3e20235-122688

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 225
-Section S99
-Paragraph 1
-Subparagraph (SX 210.7-04.2)
-URI http://asc.fasb.org/extlink&oid=6879464&loc=d3e573970-122913

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Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

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