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Pension and Other Postretirement Plans (Profit Sharing) - Additional Information (Detail) - USD ($) $ in Millions | 12 Months Ended
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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 + References No definition available. + Details
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- Definition Profit Sharing Plan, Percentage of Pre-Tax Earnings Paid + References No definition available. + Details
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