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Employee Benefit Plans - Weighted Average Asset Allocations by Asset Category (Detail)	Dec. 31, 2020	Dec. 31, 2019
Schedule of Defined Benefit Plan Asset Allocation Targets [Line Items]
Actual Asset Allocation as of December 31 (percentage)	100.00%	100.00%
Target Asset (percentage)	100.00%
Equity securities
Schedule of Defined Benefit Plan Asset Allocation Targets [Line Items]
Actual Asset Allocation as of December 31 (percentage)	34.00%	34.00%
Target Asset (percentage)	32.00%
Debt securities
Schedule of Defined Benefit Plan Asset Allocation Targets [Line Items]
Actual Asset Allocation as of December 31 (percentage)	44.00%	43.00%
Target Asset (percentage)	49.00%
Insurance (annuity) contracts
Schedule of Defined Benefit Plan Asset Allocation Targets [Line Items]
Actual Asset Allocation as of December 31 (percentage)	12.00%	12.00%
Target Asset (percentage)	12.00%
Real estate
Schedule of Defined Benefit Plan Asset Allocation Targets [Line Items]
Actual Asset Allocation as of December 31 (percentage)	8.00%	10.00%
Target Asset (percentage)	4.00%
Other
Schedule of Defined Benefit Plan Asset Allocation Targets [Line Items]
Actual Asset Allocation as of December 31 (percentage)	2.00%	1.00%
Target Asset (percentage)	3.00%

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- Definition

Schedule of Defined Benefit Plan Asset Allocation Targets [Line Items]

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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=118257860&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
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-URI http://asc.fasb.org/extlink&oid=118255775&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
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-URI http://asc.fasb.org/extlink&oid=118255775&loc=d3e1928-114920

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