Pension and Postretirement Benefits - Additional Information (Detail) - USD ($)	9 Months Ended
Sep. 30, 2020	Dec. 31, 2020
Qualified Pension Plan
Defined Benefit Plan Disclosure [Line Items]
Contribution made to qualified pension plans	$ 75,000,000.0
Estimated contribution to pension plans, remainder of financal year	$ 0
Nonqualified Pension Plan \| Underfunded Pension Plan \| Forecast
Defined Benefit Plan Disclosure [Line Items]
Estimated contribution to pension plans		$ 14,400,000

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Amount of contributions received and expected to be received by defined benefit plan from employer in current fiscal year.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
-SubTopic 20
-Section 50
-Paragraph 6
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=118255775&loc=d3e2709-114920

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Amount of contributions expected to be received by defined benefit plan from employer in fiscal year. Excludes contributions paid by employer in current fiscal year.

+ References

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- Definition

Amount of discretionary contributions made by an employer to a defined contribution plan.

+ References

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