Joint Ventures	12 Months Ended
Dec. 31, 2018
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. Stockholders’ equity includes undistributed earnings of investees accounted for under the equity method of accounting of approximately $24 million at December 31, 2018. Majority-Owned Joint Ventures STAL: 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, 2018 were $35.0 million. Next Gen Alloys LLC: 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. Next Gen Alloys LLC funds its’ development activities through the sale of shares to the two joint venture partners, and in 2018 the Company received $2.7 million from sales of noncontrolling interests to its joint venture partner, which is reported as a financing activity on the consolidated statements of cash flows. Cash and cash equivalents held by this joint venture as of December 31, 2018 were $10.1 million. Equity Method Joint Ventures A&T Stainless: On March 1, 2018, the Company announced the formation of the Allegheny & Tsingshan Stainless (A&T Stainless) joint venture with an affiliate company of Tsingshan Group (Tsingshan) to produce 60-inch wide stainless sheet products for sale in North America. Tsingshan purchased a 50% joint venture interest in A&T Stainless for $17.5 million, of which $12.0 million was received in 2018 and reported as a financing activity on the consolidated statements of cash flows. The A&T Stainless operations include the Company’s previously-idled direct roll and pickle (DRAP) facility in Midland, PA. ATI provides hot-rolling conversion services to A&T Stainless using the FRP segment’s Hot-Rolling and Processing Facility. As a result of this sale of a 50% noncontrolling interest and the subsequent deconsolidation of the A&T Stainless entity, the Company recognized a $15.9 million gain during the first quarter of 2018 under deconsolidation and derecognition accounting guidance covering the loss of control of a subsidiary determined to be a business. The gain, including ATI’s retained 50% share, was based on the fair value of the joint venture, as determined by the cash purchase price for the noncontrolling interest, and is reported in other income, net on the consolidated statement of operations, and is excluded from FRP segment results. Following this deconsolidation, ATI accounts for the A&T Stainless joint venture under the equity method of accounting. ATI’s share of the A&T Stainless joint venture results was a $3.9 million loss for the fiscal year ended December 31, 2018, which is included in the FRP segment’s operating results, and within other income, net, on the consolidated statements of operations. In late March 2018, ATI filed for an exclusion from the recently enacted Section 232 tariffs on behalf of the A&T Stainless JV, which imports semi-finished stainless slab products from Indonesia. In the absence of an exclusion, these slabs are subject to the 25% tariff levied on all stainless steel products imported into the United States. The Company continues to work within the U.S. Commerce Department’s Section 232 tariff exclusion request process to secure an exclusion on behalf of the A&T Stainless joint venture. 2018 results of A&T Stainless were negatively impacted by these tariffs. Sales to A&T Stainless, which are included in ATI’s consolidated statement of operations for the 2018 fiscal year, were $4.1 million. At December 31, 2018, accounts receivable from A&T Stainless were $0.6 million and a receivable for short-term advances for ATI’s funding of the A&T Stainless joint venture during its production ramp-up, which is reported in prepaid expenses and other assets on the consolidated balance sheet and within operating activities on the consolidated cash flow statement, was $10.5 million. Uniti: 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 was $2.9 million in 2018, $0.6 million in 2017, and $0.5 million in 2016, which is included in FRP segment’s operating results, and within other income, net in fiscal year ended December 31, 2018 on the consolidated statement of operations. This equity income is classified in cost of sales for the fiscal years ended December 31, 2017 and 2016 on the consolidated statements of operations. Sales to Uniti, which are included in ATI’s consolidated statements of operations, were $49.4 million in 2018, $38.6 million in 2017, and $20.3 million in 2016. Accounts receivable from Uniti were $1.8 million and $1.2 million at December 31, 2018 and 2017, respectively.

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. Stockholders’ equity includes undistributed earnings of investees accounted for under the equity method of accounting of approximately $24 million at December 31, 2018.

Majority-Owned Joint Ventures

STAL:

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, 2018 were $35.0 million.

Next Gen Alloys LLC:

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. Next Gen Alloys LLC funds its’ development activities through the sale of shares to the two joint venture partners, and in 2018 the Company received $2.7 million from sales of noncontrolling interests to its joint venture partner, which is reported as a financing activity on the consolidated statements of cash flows. Cash and cash equivalents held by this joint venture as of December 31, 2018 were $10.1 million.

Equity Method Joint Ventures

A&T Stainless:

On March 1, 2018, the Company announced the formation of the Allegheny & Tsingshan Stainless (A&T Stainless) joint venture with an affiliate company of Tsingshan Group (Tsingshan) to produce 60-inch wide stainless sheet products for sale in North America. Tsingshan purchased a 50% joint venture interest in A&T Stainless for $17.5 million, of which $12.0 million was received in 2018 and reported as a financing activity on the consolidated statements of cash flows. The A&T Stainless operations include the Company’s previously-idled direct roll and pickle (DRAP) facility in Midland, PA. ATI provides hot-rolling conversion services to A&T Stainless using the FRP segment’s Hot-Rolling and Processing Facility. As a result of this sale of a 50% noncontrolling interest and the subsequent deconsolidation of the A&T Stainless entity, the Company recognized a $15.9 million gain during the first quarter of 2018 under deconsolidation and derecognition accounting guidance covering the loss of control of a subsidiary determined to be a business. The gain, including ATI’s retained 50% share, was based on the fair value of the joint venture, as determined by the cash purchase price for the noncontrolling interest, and is reported in other income, net on the consolidated statement of operations, and is excluded from FRP segment results. Following this deconsolidation, ATI accounts for the A&T Stainless joint venture under the equity method of accounting.

ATI’s share of the A&T Stainless joint venture results was a $3.9 million loss for the fiscal year ended December 31, 2018, which is included in the FRP segment’s operating results, and within other income, net, on the consolidated statements of operations. In late March 2018, ATI filed for an exclusion from the recently enacted Section 232 tariffs on behalf of the A&T Stainless JV, which imports semi-finished stainless slab products from Indonesia. In the absence of an exclusion, these slabs are subject to the 25% tariff levied on all stainless steel products imported into the United States. The Company continues to work within the U.S. Commerce Department’s Section 232 tariff exclusion request process to secure an exclusion on behalf of the A&T Stainless joint venture. 2018 results of A&T Stainless were negatively impacted by these tariffs. Sales to A&T Stainless, which are included in ATI’s consolidated statement of operations for the 2018 fiscal year, were $4.1 million. At December 31, 2018, accounts receivable from A&T Stainless were $0.6 million and a receivable for short-term advances for ATI’s funding of the A&T Stainless joint venture during its production ramp-up, which is reported in prepaid expenses and other assets on the consolidated balance sheet and within operating activities on the consolidated cash flow statement, was $10.5 million.

Uniti:

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 was $2.9 million in 2018, $0.6 million in 2017, and $0.5 million in 2016, which is included in FRP segment’s operating results, and within other income, net in fiscal year ended December 31, 2018 on the consolidated statement of operations. This equity income is classified in cost of sales for the fiscal years ended December 31, 2017 and 2016 on the consolidated statements of operations. Sales to Uniti, which are included in ATI’s consolidated statements of operations, were $49.4 million in 2018, $38.6 million in 2017, and $20.3 million in 2016. Accounts receivable from Uniti were $1.8 million and $1.2 million at December 31, 2018 and 2017, respectively.