Equity and Cash Incentive Program - Fair Value Used in Determining Compensation Cost of Performance Shares (Detail) - Performance Share Awards [Member] - $ / shares	12 Months Ended
Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Fair value per share at date of grant	$ 79.28	$ 57.25	$ 73.28
Average attainment rate reflected in expense	0.00%	0.00%	0.00%

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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