Summary of Portfolio of Securities Available for Sale and Equity Investments with Readily Determinable Fair Values (Parenthetical) (Detail) - USD ($) $ in Millions	Jun. 30, 2018	Dec. 31, 2017
Available-for-sale Securities
Schedule of Available-for-sale Securities [Line Items]
Non-credit portion of OTTI recorded in AOCL, pre-tax	$ 8.6	$ 8.6

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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