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Retirement Plans - Defined Benefit Plan, Fair Value Measurement of Plan Assets (Parenthetical) (Detail) - Mutual Fund [Member]	Dec. 31, 2020	Dec. 31, 2019
Large Cap US Companies Common Stock [Member] | Retiree Healthcare Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Components of plan asset categories	36.00%	35.00%
International Growth Companies [Member] | Retiree Healthcare Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Components of plan asset categories	31.00%	29.00%
International Growth Companies [Member] | Non-U.S. Pension Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Components of plan asset categories	19.00%	23.00%
Fixed Income Bonds [Member] | Retiree Healthcare Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Components of plan asset categories	33.00%	36.00%
International Bonds [Member] | Non-U.S. Pension Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Components of plan asset categories	64.00%	57.00%
Other Investment Companies [Member] | Non-U.S. Pension Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Components of plan asset categories	17.00%	20.00%

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- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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No definition available.

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- Definition

The percentage of the fair value of investment to the fair value of total plan asset category held as of the measurement date.

+ References

No definition available.

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