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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
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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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