Joint Ventures	12 Months Ended
Dec. 31, 2017
Equity Method Investments and Joint Ventures [Abstract]
Joint Ventures	Joint Ventures The financial results of majority-owned joint ventures are consolidated into the Company’s operating results and financial position, with the minority ownership interest recognized in the consolidated statement of operations as net income attributable to noncontrolling interests, and as equity attributable to the noncontrolling interests within total stockholders’ equity. Investments in which the Company exercises significant influence, but which it does not control (generally a 20% to 50% ownership interest) are accounted for under the equity method of accounting. Majority-Owned Joint Ventures The Company has a 60% interest in the Chinese joint venture known as Shanghai STAL Precision Stainless Steel Company Limited (STAL). The remaining 40% interest in STAL is owned by China Baowu Steel Group Corporation Limited, a state authorized investment company whose equity securities are publicly traded in the People’s Republic of China. STAL is part of ATI's Flat Rolled Products segment, and manufactures Precision Rolled Strip stainless products mainly for the electronics, communication equipment, computers and automotive markets located in Asia. Cash and cash equivalents held by STAL as of December 31, 2017 were $26.2 million. During 2017, the Company formed Next Gen Alloys LLC, a joint venture with GE Aviation for the development of a new meltless titanium alloy powder manufacturing technology. ATI owns a 51% interest in this joint venture. The titanium alloy powders are being developed for use in additive manufacturing applications, including 3D printing. Cash and cash equivalents held by this joint venture as of December 31, 2017 were $7.0 million. Equity Method Joint Ventures ATI has a 50% interest in the industrial titanium joint venture known as Uniti LLC (Uniti), with the remaining 50% interest held by VSMPO, a Russian producer of titanium, aluminum, and specialty steel products. Uniti is accounted for under the equity method of accounting. ATI’s share of Uniti’s income/(loss) was $0.6 million in 2017, $0.5 million in 2016, and $(0.1) million in 2015, which is included in the Flat Rolled Products segment’s operating results, and within cost of sales in the consolidated statements of operations. Sales to Uniti, which are included in ATI’s consolidated statements of operations, were $38.6 million in 2017, $20.3 million in 2016, and $55.4 million in 2015. Accounts receivable from Uniti were $1.2 million and $1.5 million at December 31, 2017 and 2016, respectively. Stockholders’ equity includes undistributed earnings of investees accounted for under the equity method of accounting of approximately $10 million at December 31, 2017.

Joint Ventures

The financial results of majority-owned joint ventures are consolidated into the Company’s operating results and financial position, with the minority ownership interest recognized in the consolidated statement of operations as net income attributable to noncontrolling interests, and as equity attributable to the noncontrolling interests within total stockholders’ equity. Investments in which the Company exercises significant influence, but which it does not control (generally a 20% to 50% ownership interest) are accounted for under the equity method of accounting.

Majority-Owned Joint Ventures

The Company has a 60% interest in the Chinese joint venture known as Shanghai STAL Precision Stainless Steel Company Limited (STAL). The remaining 40% interest in STAL is owned by China Baowu Steel Group Corporation Limited, a state authorized investment company whose equity securities are publicly traded in the People’s Republic of China. STAL is part of ATI's Flat Rolled Products segment, and manufactures Precision Rolled Strip stainless products mainly for the electronics, communication equipment, computers and automotive markets located in Asia. Cash and cash equivalents held by STAL as of December 31, 2017 were $26.2 million.

During 2017, the Company formed Next Gen Alloys LLC, a joint venture with GE Aviation for the development of a new meltless titanium alloy powder manufacturing technology. ATI owns a 51% interest in this joint venture. The titanium alloy powders are being developed for use in additive manufacturing applications, including 3D printing. Cash and cash equivalents held by this joint venture as of December 31, 2017 were $7.0 million.

Equity Method Joint Ventures

ATI has a 50% interest in the industrial titanium joint venture known as Uniti LLC (Uniti), with the remaining 50% interest held by VSMPO, a Russian producer of titanium, aluminum, and specialty steel products. Uniti is accounted for under the equity method of accounting. ATI’s share of Uniti’s income/(loss) was $0.6 million in 2017, $0.5 million in 2016, and $(0.1) million in 2015, which is included in the Flat Rolled Products segment’s operating results, and within cost of sales in the consolidated statements of operations. Sales to Uniti, which are included in ATI’s consolidated statements of operations, were $38.6 million in 2017, $20.3 million in 2016, and $55.4 million in 2015. Accounts receivable from Uniti were $1.2 million and $1.5 million at December 31, 2017 and 2016, respectively.

Stockholders’ equity includes undistributed earnings of investees accounted for under the equity method of accounting of approximately $10 million at December 31, 2017.