v3.20.4

Postretirement Benefit Plans - Summary of Actual Pension Plan Asset Allocation (Detail)	Dec. 31, 2020	Dec. 31, 2019
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

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+ References

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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

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