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Retirement Plans - Defined Benefit Plan, Fair Value Measurement of Plan Assets (Parenthetical) (Detail) - Mutual Fund [Member]	Dec. 31, 2018	Dec. 31, 2017
Large Cap US Companies Common Stock [Member] | Retiree Healthcare Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Components of plan asset categories	40.00%	41.00%
Large Cap US Companies Common Stock [Member] | U.S. Pension Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Components of plan asset categories		45.00%
International Growth Companies [Member] | Retiree Healthcare Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Components of plan asset categories	21.00%	24.00%
International Growth Companies [Member] | Non-U.S. Pension Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Components of plan asset categories	24.00%	32.00%
International Growth Companies [Member] | U.S. Pension Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Components of plan asset categories		30.00%
Fixed Income Bonds [Member] | Retiree Healthcare Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Components of plan asset categories	39.00%	35.00%
Fixed Income Bonds [Member] | Non-U.S. Pension Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Components of plan asset categories	56.00%	58.00%
Fixed Income Bonds [Member] | U.S. Pension Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Components of plan asset categories		25.00%
Mortgages [Member] | Non-U.S. Pension Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Components of plan asset categories		1.00%
Other Investment Companies [Member] | Non-U.S. Pension Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Components of plan asset categories	20.00%	9.00%

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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.

+ References

No definition available.

+ Details

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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.

+ Details

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- Details

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