Restructuring - Restructuring Activities Including Merak Facility Closure (Detail) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Mar. 31, 2016	Dec. 31, 2015	Mar. 31, 2016
Restructuring Cost And Reserve [Line Items]
Reserve balance	$ 22	$ 9	$ 9
Charges	(5)		43
Cash paid	(2)		(9)
Reserve balance	13	22	13
Severance and Employee Benefits [Member]
Restructuring Cost And Reserve [Line Items]
Reserve balance	19	5	5
Charges	1		26
Cash paid	(9)		(20)
Reserve balance	11	19	11
Asset Impairment and Accelerated Depreciation [Member]
Restructuring Cost And Reserve [Line Items]
Charges	1		23
Other [Member]
Restructuring Cost And Reserve [Line Items]
Reserve balance	1	2	2
Charges	1		3
Cash paid	(2)		(5)
Reserve balance		1
2016 Plan [Member]
Restructuring Cost And Reserve [Line Items]
Reserve balance	16
Charges	3	48
Costs charged against liabilities / (assets)	(1)	(21)
Cash paid	(9)	(11)
Reserve balance	9	16	9
2016 Plan [Member] | Severance and Employee Benefits [Member]
Restructuring Cost And Reserve [Line Items]
Reserve balance	16
Charges		25
Costs charged against liabilities / (assets)		1
Cash paid	(7)	(10)
Reserve balance	9	16	$ 9
2016 Plan [Member] | Asset Impairment and Accelerated Depreciation [Member]
Restructuring Cost And Reserve [Line Items]
Charges	1	22
Costs charged against liabilities / (assets)	(1)	(22)
2016 Plan [Member] | Other [Member]
Restructuring Cost And Reserve [Line Items]
Charges	2	1
Cash paid	$ (2)	$ (1)