Investments in fixed maturity securities - Narrative (Detail)	Mar. 31, 2018
Foreign governments [Member] \| AA or Higher Credit Rating [Member]
Summary of Investment Holdings [Line Items]
Percentage of fixed maturity investments by credit rating	89.00%

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.

No definition available.

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