Stock-based Compensation Plans - PG/RG-PSUs Activities (Parenthetical) (Detail) - Performance-based PG-PSUs and RG-PSUs	12 Months Ended
Dec. 31, 2017
Minimum
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Potential payout of shares granted	0.00%
Maximum
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Potential payout of shares granted	150.00%

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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