Pension Plans, Other Postretirement Benefits, and Defined-Contribution Plans - Effects of 1% Change in the Assumed Health Care Cost Trend Rate Table (Detail) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2012
Defined Benefit Plan, Effect of One-Percentage Point Change in Assumed Health Care Cost Trend Rates [Abstract]
Effect of one percentage point increase on total of service and interest cost components	$ 3
Effect of one percentage point increase on other postretirement benefit obligation	28
Effect of one percentage point decrease on total of service and interest cost components	(2)
Effect of one percentage point decrease on other postretirement benefit obligation	$ (24)