Segment information Segment Information (narrative Detail (Details) - USD ($) $ in Millions	3 Months Ended
Mar. 31, 2018	Mar. 31, 2017
Segment Reporting Information [Line Items]
Gain (Loss) on Derivative	$ 79	$ 27
Net investment income	806	745
North America Agricultural Insurance [Member]
Segment Reporting Information [Line Items]
Segment Income Loss Including Gains Losses On Crop Derivatives	102
Gain (Loss) on Derivative	2
Net investment income	7	6
Segment Life [Member]
Segment Reporting Information [Line Items]
Net investment income	83	$ 75
Management Underwriting Income (Loss)	67
Gains Losses On Fair Value Changes In Separate Account Assets	$ 6

Gains Losses On Fair Value Changes In Separate Account Assets

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- Definition

Management Underwriting Income Loss Insurance

+ References

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- Definition

Segment Income Loss Including Gains Losses On Crop Derivatives

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- Definition

Amount of increase (decrease) in the fair value of derivatives recognized in the income statement.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 50
-Paragraph 4A
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=84234895&loc=SL5618551-113959

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-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 50
-Paragraph 4C
-Subparagraph (a),(c),(d),(e)
-URI http://asc.fasb.org/extlink&oid=84234895&loc=SL5624171-113959

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Amount, after investment expense, of income earned from investments in securities and real estate. Includes, but is not limited to, real estate investment, policy loans, dividends, and interest. Excludes realized gain (loss) on investments.

+ References

Reference 1: 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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-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 235
-Section S99
-Paragraph 1
-Subparagraph (SX 210.12-16(Column G))
-URI http://asc.fasb.org/extlink&oid=34713774&loc=d3e574960-122915

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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.

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