Investments in fixed maturity securities - Narrative (Detail) - Fixed Maturities [Member] - USD ($) $ in Millions	Sep. 30, 2015	Dec. 31, 2014
Summary of Investment Holdings [Line Items]
Unrealized losses related to securities that have been in an unrealized loss position for more than 12 months	$ 10	$ 15
Foreign governments [Member] \| United Kingdom, Germany, Australia, Canada or The Netherlands [Member]
Summary of Investment Holdings [Line Items]
Percentage of fixed maturity investments by geographic location	75.00%
Foreign governments [Member] \| AA or Higher Credit Rating [Member]
Summary of Investment Holdings [Line Items]
Percentage of fixed maturity investments by credit rating	94.00%

The percentage of available-for-sale debt securities portfolio as of the reporting date having a specified credit rating.

No definition available.

+ Details

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- Definition

The percentage of the available-for-sale debt securities portfolio as of the reporting date that originate from or are guaranteed by a specified country or countries.

+ References

No definition available.

+ Details

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- Definition

Amount of accumulated unrealized loss on investments in debt and equity securities classified as available-for-sale that have been in a continuous loss position for twelve months or longer.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 320

-SubTopic 10

-Section 50

-Paragraph 6

-Subparagraph (a)(2)

-URI http://asc.fasb.org/extlink&oid=27724398&loc=d3e27290-111563

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 320

-SubTopic 10

-Section 50

-Paragraph 7

-URI http://asc.fasb.org/extlink&oid=27724398&loc=d3e27337-111563

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- Definition

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

No definition available.

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