Pension and Other Postretirement Plans (Profit Sharing) - Additional Information (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Deferred Compensation Arrangement with Individual, Postretirement Benefits [Line Items]
Profit sharing and payroll tax expense	$ 628	$ 698	$ 235
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%