Weighted Average Asset Allocation for Pension Plans and Target Allocation (Detail)	Dec. 31, 2017	Dec. 31, 2016
Defined Benefit Plan Disclosure [Line Items]
Target Allocation	100.00%
Actual Allocation	100.00%	100.00%
Equity Securities
Defined Benefit Plan Disclosure [Line Items]
Target Allocation	58.00%
Equity Securities \| United States
Defined Benefit Plan Disclosure [Line Items]
Target Allocation	49.00%
Actual Allocation	47.00%	47.00%
Equity Securities \| International
Defined Benefit Plan Disclosure [Line Items]
Target Allocation	9.00%
Actual Allocation	10.00%	10.00%
Debt securities
Defined Benefit Plan Disclosure [Line Items]
Target Allocation	42.00%
Actual Allocation	42.00%	42.00%
Cash and cash equivalents
Defined Benefit Plan Disclosure [Line Items]
Target Allocation	0.00%
Actual Allocation	1.00%	1.00%

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Percentage of target investment allocation to total plan assets. Includes, but is not limited to, percentage on weighted-average basis if more than one plan.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
-SubTopic 20
-Section 50
-Paragraph 1
-Subparagraph (d)(5)(i)
-URI http://asc.fasb.org/extlink&oid=82843861&loc=d3e1928-114920

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Percentage of fair value of investments (categorized by debt securities, equity securities, real estate and other plan assets) to the fair value of plan assets held.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
-SubTopic 20
-Section 50
-Paragraph 5
-Subparagraph (c)
-URI http://asc.fasb.org/extlink&oid=82843861&loc=d3e2446-114920

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
-SubTopic 20
-Section 50
-Paragraph 1
-Subparagraph (d)(1)
-URI http://asc.fasb.org/extlink&oid=82843861&loc=d3e1928-114920

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