Investments (Net investment income) (Details) - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Net Investment Income [Line Items]
Gross investment income	$ 2,047	$ 1,903	$ 2,125
Investment expense	(59)	(63)	(58)
Net Investment Income	1,988	1,840	2,067
Fixed maturity securities [Member]
Net Investment Income [Line Items]
Gross investment income	1,819	1,751	1,803
Total equity securities available-for-sale [Member]
Net Investment Income [Line Items]
Gross investment income	10	12	12
Limited partnership investments [Member]
Net Investment Income [Line Items]
Gross investment income	155	92	263
Mortgage loans [Member]
Net Investment Income [Line Items]
Gross investment income	41	33	31
Short term investments [Member]
Net Investment Income [Line Items]
Gross investment income	8	6	3
Trading portfolio [Member]
Net Investment Income [Line Items]
Gross investment income	10	8	10
Other [Member]
Net Investment Income [Line Items]
Gross investment income	$ 4	$ 1	$ 3

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

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- Definition

The income earned from investments in securities and property, equipment and other capital assets. It includes rent from property and equipment, dividends from shares in corporations, and interest from bonds, loans, mortgages, derivatives, commercial paper, bank accounts, certificates of deposits, treasuries, and other financial securities. It also includes realized gains and 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=63488584&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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