Pension and Other Benefit Plans - Weighted-Average Allocation of Plan Assets and Target Allocation by Asset Category (Detail)	Dec. 31, 2020	Dec. 31, 2019
US
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
Defined Benefit Plan Disclosure [Line Items]
Target allocation of assets	15.00%	22.00%
Equity securities | US | Minimum
Defined Benefit Plan Disclosure [Line Items]
Target Allocation Percentage of Assets	20.00%
Equity securities | US | Maximum
Defined Benefit Plan Disclosure [Line Items]
Target Allocation Percentage of Assets	30.00%
Equity securities | International
Defined Benefit Plan Disclosure [Line Items]
Target allocation of assets	43.00%	50.00%
Equity securities | International | Minimum
Defined Benefit Plan Disclosure [Line Items]
Target Allocation Percentage of Assets		47.00%
Equity securities | International | Maximum
Defined Benefit Plan Disclosure [Line Items]
Target Allocation Percentage of Assets		59.00%
Debt securities | US
Defined Benefit Plan Disclosure [Line Items]
Target allocation of assets	76.00%	70.00%
Debt securities | US | Minimum
Defined Benefit Plan Disclosure [Line Items]
Target Allocation Percentage of Assets	63.00%
Debt securities | US | Maximum
Defined Benefit Plan Disclosure [Line Items]
Target Allocation Percentage of Assets	77.00%
Debt securities | International
Defined Benefit Plan Disclosure [Line Items]
Target allocation of assets	36.00%	31.00%
Debt securities | International | Minimum
Defined Benefit Plan Disclosure [Line Items]
Target Allocation Percentage of Assets		27.00%
Debt securities | International | Maximum
Defined Benefit Plan Disclosure [Line Items]
Target Allocation Percentage of Assets		33.00%
Cash and cash equivalents | US
Defined Benefit Plan Disclosure [Line Items]
Target allocation of assets	3.00%	2.00%
Cash and cash equivalents | US | Minimum
Defined Benefit Plan Disclosure [Line Items]
Target Allocation Percentage of Assets	0.00%
Cash and cash equivalents | US | Maximum
Defined Benefit Plan Disclosure [Line Items]
Target Allocation Percentage of Assets	3.00%
Cash and cash equivalents | International
Defined Benefit Plan Disclosure [Line Items]
Target allocation of assets	4.00%	4.00%
Cash and cash equivalents | International | Minimum
Defined Benefit Plan Disclosure [Line Items]
Target Allocation Percentage of Assets		0.00%
Cash and cash equivalents | International | Maximum
Defined Benefit Plan Disclosure [Line Items]
Target Allocation Percentage of Assets		3.00%
Alternative investments | US
Defined Benefit Plan Disclosure [Line Items]
Target allocation of assets	6.00%	6.00%
Alternative investments | US | Minimum
Defined Benefit Plan Disclosure [Line Items]
Target Allocation Percentage of Assets	5.00%
Alternative investments | US | Maximum
Defined Benefit Plan Disclosure [Line Items]
Target Allocation Percentage of Assets	10.00%
Alternative investments | International
Defined Benefit Plan Disclosure [Line Items]
Target allocation of assets	17.00%	15.00%
Alternative investments | International | Minimum
Defined Benefit Plan Disclosure [Line Items]
Target Allocation Percentage of Assets		15.00%
Alternative investments | International | Maximum
Defined Benefit Plan Disclosure [Line Items]
Target Allocation Percentage of Assets		22.00%