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Postretirement Benefit Plans - Asset Allocations of Postretirement Benefit Plans (Detail) | Dec. 31, 2017
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Minimum | Cash and cash equivalents |
Defined Benefit Plan Disclosure [Line Items] |
Defined benefit plan, target allocation percentage of assets | 0.00%
Minimum | Equity |
Defined Benefit Plan Disclosure [Line Items] |
Defined benefit plan, target allocation percentage of assets | 15.00%
Minimum | Fixed income |
Defined Benefit Plan Disclosure [Line Items] |
Defined benefit plan, target allocation percentage of assets | 10.00%
Minimum | Private equity funds |
Defined Benefit Plan Disclosure [Line Items] |
Defined benefit plan, target allocation percentage of assets | 0.00%
Minimum | Real estate funds |
Defined Benefit Plan Disclosure [Line Items] |
Defined benefit plan, target allocation percentage of assets | 0.00%
Minimum | Hedge funds |
Defined Benefit Plan Disclosure [Line Items] |
Defined benefit plan, target allocation percentage of assets | 0.00%
Minimum | Commodities |
Defined Benefit Plan Disclosure [Line Items] |
Defined benefit plan, target allocation percentage of assets | 0.00%
Maximum | Cash and cash equivalents |
Defined Benefit Plan Disclosure [Line Items] |
Defined benefit plan, target allocation percentage of assets | 20.00%
Maximum | Equity |
Defined Benefit Plan Disclosure [Line Items] |
Defined benefit plan, target allocation percentage of assets | 65.00%
Maximum | Fixed income |
Defined Benefit Plan Disclosure [Line Items] |
Defined benefit plan, target allocation percentage of assets | 60.00%
Maximum | Private equity funds |
Defined Benefit Plan Disclosure [Line Items] |
Defined benefit plan, target allocation percentage of assets | 15.00%
Maximum | Real estate funds |
Defined Benefit Plan Disclosure [Line Items] |
Defined benefit plan, target allocation percentage of assets | 10.00%
Maximum | Hedge funds |
Defined Benefit Plan Disclosure [Line Items] |
Defined benefit plan, target allocation percentage of assets | 20.00%
Maximum | Commodities |
Defined Benefit Plan Disclosure [Line Items] |
Defined benefit plan, target allocation percentage of assets | 15.00%

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- Definition 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. + References No definition available. + Details
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- Definition 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 + Details
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