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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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