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Actual Investment Allocations (Detail)

Dec. 31, 2019

Dec. 31, 2018

Dec. 31, 2017

Dec. 31, 2016

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

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

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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

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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=108410482&loc=d3e1928-114920

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