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Pension Plans and Postretirement Benefits - Plan Asset Allocations by Asset Category (Detail) | Dec. 31, 2020 | Dec. 31, 2019
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UNITED STATES | Pension Plan |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Total | 100.00% | 100.00%
UNITED STATES | Pension Plan | Commingled and Mutual Funds |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Total | 29.00% | 27.00%
UNITED STATES | Pension Plan | U.S. Government Securities |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Total | 28.00% | 22.00%
UNITED STATES | Pension Plan | Fixed Income (excluding U.S. Government Securities) |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Total | 18.00% | 33.00%
UNITED STATES | Pension Plan | Diversified Credit |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Total | 11.00% | 5.00%
UNITED STATES | Pension Plan | Real Estate |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Total | 7.00% | 7.00%
UNITED STATES | Pension Plan | Partnerships with Security Holdings |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Total | 4.00% | 5.00%
UNITED STATES | Pension Plan | Other |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Total | 3.00% | 1.00%
Canada | Other Benefits |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Total | 100.00% | 100.00%
Canada | Other Benefits | Equity Securities and Commingled Mutual Funds |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Total | 0.00% | 35.00%
Canada | Other Benefits | Fixed Income |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Total | 98.00% | 62.00%
Canada | Other Benefits | Other |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Total | 2.00% | 3.00%

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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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