Pension and Postretirement Benefit Plans and Defined Contribution Plans - One-Percentage-Point Increase or Decrease in the Healthcare Cost Trend Rate (Detail) - Postretirement Plans [Member] $ in Millions	12 Months Ended
	Dec. 31, 2015 USD ($)
Defined Benefit Plan Disclosure [Line Items]
Effect on total service and interest cost components, increase	$ 11
Effect on total service and interest cost components, decrease	(11)
Effect on postretirement benefit obligation, increase	77
Effect on postretirement benefit obligation, decrease	$ (80)