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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) |  |  |  |

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