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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- Definition

Description of target allocation percentages, or range of percentages, considering the major categories of plan assets as of the latest statement of financial position presented (on a weighted-average basis for employers with more than one plan) that are pertinent to an understanding of the plan investment policies and strategies.

+ 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)(i)
-URI http://asc.fasb.org/extlink&oid=82843861&loc=d3e1928-114920

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
-SubTopic 20
-Section 50
-Paragraph 5
-Subparagraph (c)(i)
-URI http://asc.fasb.org/extlink&oid=82843861&loc=d3e2446-114920

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- Definition

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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Postretirement Benefit Plans - Asset Allocation Range (Detail)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
U.S. equities [Member]
Defined Benefit Plan Disclosure [Line Items]
Actual allocation	22.00%	26.00%
International equities [Member]
Defined Benefit Plan Disclosure [Line Items]
Actual allocation	8.00%	22.00%
Fixed income [Member]
Defined Benefit Plan Disclosure [Line Items]
Actual allocation	68.00%	51.00%
Cash and other [Member]
Defined Benefit Plan Disclosure [Line Items]
Actual allocation	2.00%	1.00%
Minimum [Member] \| U.S. equities [Member]
Defined Benefit Plan Disclosure [Line Items]
Asset Allocation Range	0
Minimum [Member] \| International equities [Member]
Defined Benefit Plan Disclosure [Line Items]
Asset Allocation Range	0
Minimum [Member] \| Fixed income [Member]
Defined Benefit Plan Disclosure [Line Items]
Asset Allocation Range	0.5
Minimum [Member] \| Cash and other [Member]
Defined Benefit Plan Disclosure [Line Items]
Asset Allocation Range	0.00
Maximum [Member] \| U.S. equities [Member]
Defined Benefit Plan Disclosure [Line Items]
Asset Allocation Range	0.5
Maximum [Member] \| International equities [Member]
Defined Benefit Plan Disclosure [Line Items]
Asset Allocation Range	0.25
Maximum [Member] \| Fixed income [Member]
Defined Benefit Plan Disclosure [Line Items]
Asset Allocation Range	1
Maximum [Member] \| Cash and other [Member]
Defined Benefit Plan Disclosure [Line Items]
Asset Allocation Range	0.1