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Pension and Other Postretirement Plans (Profit Sharing) - Additional Information (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Deferred Compensation Arrangement with Individual, Postretirement Benefits [Line Items]
Profit sharing and payroll tax expense	$ 349	$ 628	$ 698
Minimum
Deferred Compensation Arrangement with Individual, Postretirement Benefits [Line Items]
Percentage of pre-tax earnings paid for profit sharing plan	5.00%
Maximum
Deferred Compensation Arrangement with Individual, Postretirement Benefits [Line Items]
Percentage of pre-tax earnings paid for profit sharing plan	20.00%

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- Definition

Defined Benefit Plan Profit Sharing And Payroll Tax Expense

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- Definition

Profit Sharing Plan, Percentage of Pre-Tax Earnings Paid

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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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