Restructuring and Other Charges - Activity and Reserve Balances for Restructuring Charges (Parenthetical) (Detail) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Restructuring Cost and Reserve [Line Items]
Asset retirement obligations	$ 4	$ 45	$ 4	$ 45
Restructuring and other charges	$ 18	66	134	460
Pension And Other Postretirement Benefits Costs Charged To Restructuring [Member]
Restructuring Cost and Reserve [Line Items]
Other layoff cost including reclassification in pension cost				28
Environmental Remediation [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring and other charges				29
Pension Benefits [Member]
Restructuring Cost and Reserve [Line Items]
Other layoff cost including reclassification in pension cost			14
Restructuring and other charges		$ 2	$ 2	$ 2