v3.20.4

Postretirement Benefit Plans - Summary of Actual Pension Plan Asset Allocation (Detail) | Dec. 31, 2020 | Dec. 31, 2019
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Defined Benefit Plan, Plan Assets, Allocation [Line Items] |  |
Actual benefit plan asset allocation | 100.00% | 100.00%
Equity securities |  |
Defined Benefit Plan, Plan Assets, Allocation [Line Items] |  |
Actual benefit plan asset allocation | 34.00% | 31.00%
Debt securities |  |
Defined Benefit Plan, Plan Assets, Allocation [Line Items] |  |
Actual benefit plan asset allocation | 39.00% | 43.00%
Insurance contracts |  |
Defined Benefit Plan, Plan Assets, Allocation [Line Items] |  |
Actual benefit plan asset allocation | 7.00% | 7.00%
Other |  |
Defined Benefit Plan, Plan Assets, Allocation [Line Items] |  |
Actual benefit plan asset allocation | 20.00% | 19.00%

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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 actual 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/2009/role/commonPracticeRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (d)(i) -URI http://asc.fasb.org/extlink&oid=118255775&loc=d3e1928-114920 + Details
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