Fair Value Measurements of Investments Held by Retirement Plan (Parenthetical) (Detail) - Large-Cap Value - Common/Collective Trusts - Equity	Dec. 31, 2017 Stock
Minimum
Defined Benefit Plan Disclosure [Line Items]
Number of stocks held	60
Maximum
Defined Benefit Plan Disclosure [Line Items]
Number of stocks held	70

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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