Pension and Other Benefit Plans - Weighted-Average Allocation of Plan Assets and Target Allocation by Asset Category (Detail)	Dec. 31, 2017	Dec. 31, 2016
US Plan Assets
Defined Benefit Plan Disclosure [Line Items]
Target Allocation Percentage of Assets	100.00%	100.00%
Target allocation of assets	100.00%	100.00%
International
Defined Benefit Plan Disclosure [Line Items]
Target Allocation Percentage of Assets	100.00%	100.00%
Target allocation of assets	100.00%	100.00%
Equity securities | US Plan Assets
Defined Benefit Plan Disclosure [Line Items]
Target allocation of assets	51.00%	52.00%
Equity securities | US Plan Assets | Maximum
Defined Benefit Plan Disclosure [Line Items]
Target Allocation Percentage of Assets	56.00%
Equity securities | US Plan Assets | Minimum
Defined Benefit Plan Disclosure [Line Items]
Target Allocation Percentage of Assets	37.00%
Equity securities | International
Defined Benefit Plan Disclosure [Line Items]
Target allocation of assets	64.00%	64.00%
Equity securities | International | Maximum
Defined Benefit Plan Disclosure [Line Items]
Target Allocation Percentage of Assets	71.00%
Equity securities | International | Minimum
Defined Benefit Plan Disclosure [Line Items]
Target Allocation Percentage of Assets	45.00%
Debt securities | US Plan Assets
Defined Benefit Plan Disclosure [Line Items]
Target allocation of assets	38.00%	37.00%
Debt securities | US Plan Assets | Maximum
Defined Benefit Plan Disclosure [Line Items]
Target Allocation Percentage of Assets	62.00%
Debt securities | US Plan Assets | Minimum
Defined Benefit Plan Disclosure [Line Items]
Target Allocation Percentage of Assets	35.00%
Debt securities | International
Defined Benefit Plan Disclosure [Line Items]
Target allocation of assets	23.00%	25.00%
Debt securities | International | Maximum
Defined Benefit Plan Disclosure [Line Items]
Target Allocation Percentage of Assets	35.00%
Debt securities | International | Minimum
Defined Benefit Plan Disclosure [Line Items]
Target Allocation Percentage of Assets	20.00%
Cash and cash equivalents | US Plan Assets
Defined Benefit Plan Disclosure [Line Items]
Target allocation of assets	3.00%	2.00%
Cash and cash equivalents | US Plan Assets | Maximum
Defined Benefit Plan Disclosure [Line Items]
Target Allocation Percentage of Assets	3.00%
Cash and cash equivalents | US Plan Assets | Minimum
Defined Benefit Plan Disclosure [Line Items]
Target Allocation Percentage of Assets	0.00%
Cash and cash equivalents | International
Defined Benefit Plan Disclosure [Line Items]
Target allocation of assets	4.00%	2.00%
Cash and cash equivalents | International | Maximum
Defined Benefit Plan Disclosure [Line Items]
Target Allocation Percentage of Assets	5.00%
Cash and cash equivalents | International | Minimum
Defined Benefit Plan Disclosure [Line Items]
Target Allocation Percentage of Assets	0.00%
Alternative investments | US Plan Assets
Defined Benefit Plan Disclosure [Line Items]
Target allocation of assets	8.00%	9.00%
Alternative investments | US Plan Assets | Maximum
Defined Benefit Plan Disclosure [Line Items]
Target Allocation Percentage of Assets	10.00%
Alternative investments | US Plan Assets | Minimum
Defined Benefit Plan Disclosure [Line Items]
Target Allocation Percentage of Assets	0.00%
Alternative investments | International
Defined Benefit Plan Disclosure [Line Items]
Target allocation of assets	9.00%	9.00%
Alternative investments | International | Maximum
Defined Benefit Plan Disclosure [Line Items]
Target Allocation Percentage of Assets	25.00%
Alternative investments | International | Minimum
Defined Benefit Plan Disclosure [Line Items]
Target Allocation Percentage of Assets	0.00%