Retirement Plans and Other Post-Retirement Benefits - Weighted-Average Assumptions Used in Computing Benefit Obligations (Detail)	Dec. 31, 2020	Dec. 31, 2019
Pension Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Discount rate - benefit obligation	2.17%	2.70%
Other Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Discount rate - benefit obligation	2.30%	3.11%

Weighted average rate for present value of future retirement benefits cash flows, used to determine benefit obligation of defined benefit plan.

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
-SubTopic 20
-Section 50
-Paragraph 1
-Subparagraph (k)(1)
-URI http://asc.fasb.org/extlink&oid=118255775&loc=d3e1928-114920

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