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Actual Investment Allocations (Detail) | Dec. 31, 2019 | Dec. 31, 2018 | Dec. 31, 2017 | Dec. 31, 2016
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Pension Plans |  |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |
Actual Allocation |  |  | 100.00% | 100.00% | 100.00%
Pension Plans | Equity Funds |  |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |
Actual Allocation |  |  | 49.00% | 49.00% | 46.00%
Pension Plans | Fixed Income Securities |  |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |
Actual Allocation |  |  | 40.00% | 34.00% | 37.00%
Pension Plans | Asset Allocation Fund |  |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |
Actual Allocation | [1] |  |  | 6.00% | 7.00%
Pension Plans | Other |  |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |
Actual Allocation | [2] |  | 1.00% | 1.00% |
Other Postretirement Benefit Plans, Defined Benefit |  |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |
Actual Allocation |  |  | 100.00% | 100.00% | 100.00%
Other Postretirement Benefit Plans, Defined Benefit | Equity Funds |  |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |
Actual Allocation |  |  | 53.00% | 56.00% | 55.00%
Other Postretirement Benefit Plans, Defined Benefit | Fixed Income Securities |  |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |
Actual Allocation |  |  | 47.00% | 42.00% | 43.00%
Other Postretirement Benefit Plans, Defined Benefit | Other |  |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |
Actual Allocation | [3] |  |  | 2.00% | 2.00%
Real Estate Funds | Pension Plans |  |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |
Actual Allocation |  |  | 10.00% | 10.00% | 10.00%
Scenario Forecast | Pension Plans | Equity Funds |  |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |
Target Allocation |  | 53.00% |  |  |
Scenario Forecast | Pension Plans | Fixed Income Securities |  |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |
Target Allocation |  | 37.00% |  |  |
Scenario Forecast | Other Postretirement Benefit Plans, Defined Benefit | Equity Funds |  |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |
Target Allocation |  | 55.00% |  |  |
Scenario Forecast | Other Postretirement Benefit Plans, Defined Benefit | Fixed Income Securities |  |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |
Target Allocation |  | 45.00% |  |  |
Scenario Forecast | Real Estate Funds | Pension Plans |  |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |
Target Allocation |  | 10.00% |  |  |
[1] | Represents investments in an asset allocation fund. This fund invests in both equity and debt securities.
[2] | Represents investments being held in cash equivalents as of December 31, 2018 pending payment of benefits.
[3] | Represents investments being held in cash equivalents as of December 31, 2017 and 2016 pending transfer into debt and equity funds.

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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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