Investments (Net investment income) (Details) - USD ($) $ in Millions	3 Months Ended	6 Months Ended
Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015
Net Investment Income [Line Items]
Gross investment income	$ 517	$ 515	$ 966	$ 1,087
Investment expense	(15)	(15)	(29)	(29)
Net investment income	502	500	937	1,058
Fixed maturity securities [Member]
Net Investment Income [Line Items]
Gross investment income	449	452	895	895
Total equity securities available-for-sale [Member]
Net Investment Income [Line Items]
Gross investment income	4	3	7	6
Limited partnership investments [Member]
Net Investment Income [Line Items]
Gross investment income	46	48	32	162
Mortgage loans [Member]
Net Investment Income [Line Items]
Gross investment income	13	9	22	17
Short term investments [Member]
Net Investment Income [Line Items]
Gross investment income	1	0	4	2
Trading portfolio [Member]
Net Investment Income [Line Items]
Gross investment income	$ 4	$ 3	$ 6	$ 5

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

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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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