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Retirement Benefits - Weighted Average Asset Allocation for Pension Plans and Target Allocation (Detail) | Dec. 31, 2018 | Dec. 31, 2017
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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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- 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/exampleRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 55 -Paragraph 17 -URI http://asc.fasb.org/extlink&oid=112275985&loc=d3e4179-114921 Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (d)(i) -URI http://asc.fasb.org/extlink&oid=108410482&loc=d3e1928-114920 + Details
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