Restructuring and Other Charges - Activity and Reserve Balances for Restructuring Charges (Parenthetical) (Detail) - USD ($) $ in Millions	3 Months Ended		12 Months Ended
	Mar. 31, 2016	Mar. 31, 2015	Dec. 31, 2015
Restructuring Cost and Reserve [Line Items]
Other layoff cost including reclassification in pension cost	$ 20		$ 291
Restructuring and other charges	93	$ 177
Pension Costs [Member]
Restructuring Cost and Reserve [Line Items]
Other layoff cost including reclassification in pension cost	35
Asset Retirement Obligations [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring and other charges	$ 7		76
Environmental Remediation [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring and other charges			$ 86