Acquisitions and Divestitures - Additional Information (Detail) $ / shares in Units, € in Millions, $ in Millions		1 Months Ended			2 Months Ended	3 Months Ended		9 Months Ended		12 Months Ended
	Nov. 30, 2014 USD ($)	Jul. 31, 2015 shares	Mar. 31, 2015 EUR (€) Employees shares	Mar. 31, 2015 USD ($) Employees shares	Sep. 30, 2015 USD ($)	Sep. 30, 2015 USD ($)	Sep. 30, 2014 USD ($)	Sep. 30, 2015 USD ($) Tranche shares	Sep. 30, 2014 USD ($)	Dec. 31, 2014 USD ($) Employees	Mar. 31, 2015 USD ($) $ / shares	Mar. 06, 2015 $ / shares
Business Acquisition [Line Items]
Goodwill					$ 5,443	$ 5,443		$ 5,443		$ 5,247
After-tax operating income (ATOI)						410	$ 581	1,633	$ 1,309
Russia [Member]
Business Acquisition [Line Items]
Net cash received								30
Loss from divestitures before income tax								161
Net loss, after tax and noncontrolling interest								151
Stupino Titanium Company [Member]
Business Acquisition [Line Items]
Number of employees | Employees			1,870	1,870
Generated sale,net				$ 130
Tital [Member]
Business Acquisition [Line Items]
Goodwill											$ 123
Number of employees | Employees			650	650
Cash paid for business acquisition			€ 188	$ 204
Business acquisition transaction cost			€ 1								1
RTI [Member]
Business Acquisition [Line Items]
Total assets					1,747	1,747		1,747
Goodwill					209	209		209
Intangible assets					73	73		73
Total liabilities					877	877		877
Number of employees | Employees										2,600
Common stock estimated value											$ 870
Business acquisition common stock issued, price per share | $ / shares											$ 9.96	$ 14.48
Number of shares to be issued upon conversion | $ / shares											$ 2.8315
Acquisition price per share | $ / shares												$ 41
Number of common stock shares issued in a part of acquisition | shares		87,000,000	87,397,414	87,397,414
Professional fees and costs				$ 25
Professional fees and costs , after tax				$ 19
Generated sale,net										$ 794
Third-party sales					127
After-tax operating income (ATOI)					(7)
Goodwill deductible for income tax purpose					0	0		$ 0
RTI [Member] | Convertible Notes [Member]
Business Acquisition [Line Items]
Number of repayment tranches | Tranche								2
Convertible debt, due date of first tranche								Dec. 01, 2015
Convertible debt, due date of second tranche								Dec. 31, 2019
Conversion of notes to common stock | shares								37,009,898
Firth Rixson [Member]
Business Acquisition [Line Items]
Business acquisition purchase price	$ 2,995
Contingent consideration	130
Total assets	3,470
Goodwill	1,898
Intangible assets	398				$ 791	$ 791		$ 791
Total liabilities	$ 475
Properties, plants and equipment								166
Decrease in goodwill								393
Firth Rixson [Member] | Goodwill [Member]
Business Acquisition [Line Items]
Decrease in goodwill								$ (94)