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Debt - Narrative (Details) |  |  |  |  | 12 Months Ended |
--- | --- | --- | --- | --- | --- | ---
Sep. 23, 2015 USD ($) | Jun. 02, 2014 USD ($) | Jun. 01, 2014 USD ($) shares | Jul. 12, 2013 USD ($) | Dec. 31, 2015 USD ($) | Dec. 31, 2014 USD ($) | Dec. 31, 2013 USD ($) $ / shares | Aug. 15, 2015 | [1]
Interest Costs Incurred [Abstract] |  |  |  |  |  |  |  |  |  |  |
Interest expense |  |  |  |  |  | $ 111,400,000 |  | $ 109,800,000 |  | $ 66,000,000 |
Interest costs capitalized |  |  |  |  |  | 2,200,000 |  | 5,300,000 |  | 45,700,000 |
Interest costs paid |  |  |  |  |  | 113,400,000 |  | 113,200,000 |  | 110,600,000 |
Interest income |  |  |  |  |  | 1,200,000 |  | 1,100,000 |  | 800,000 |
Long-term Debt, Fiscal Year Maturity [Abstract] |  |  |  |  |  |  |  |  |  |  |
2016 |  |  |  |  |  | 3,900,000 |  |  |  |  |
2017 |  |  |  |  |  | 900,000 |  |  |  |  |
2018 |  |  |  |  |  | 200,000 |  |  |  |  |
2019 |  |  |  |  |  | 350,200,000 |  |  |  |  |
2020 |  |  |  |  |  | 0 |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |
Payments of debt issuance costs |  |  |  |  |  | 0 |  | 1,200,000 |  | $ 5,200,000 |
Allegheny Technologies $500 million 5.875% Senior Notes due 2023 [Member] |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |
Debt instrument carrying amount |  |  |  |  | $ 500,000,000 | $ 500,000,000 | [1] | $ 500,000,000 | [1] |  |
Debt instrument interest rate stated percentage |  |  |  |  |  |  |  | 6.125% |  | 5.875% | 7.625%
Debt instrument maturity date |  |  |  |  | Aug. 15, 2023 |  |  |  |  |  |
Payments of debt issuance costs |  |  |  |  |  |  |  |  |  | $ 5,200,000 |
Amortization period of debt issuance costs |  |  |  |  |  | 10 years |  |  |  |  |
Allegheny Technologies $350 million 9.375% Senior Notes due 2019 [Member] |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |
Debt instrument carrying amount |  |  |  |  |  | $ 350,000,000 |  | $ 350,000,000 |  |  |
Debt instrument interest rate stated percentage |  |  |  |  |  | 9.375% |  | 9.375% |  |  |
Allegheny Technologies $402.5 million 4.25% Convertible Senior Notes due 2014 [Member] |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |
Debt instrument carrying amount |  |  |  |  |  |  |  |  |  | $ 402,500,000 |
Debt instrument interest rate stated percentage |  |  |  |  |  |  |  |  |  | 4.25% |
Repayments of Convertible Debt |  |  | $ 397,500,000 |  |  |  |  |  |  |  |
Convertible notes, Amount converted |  |  |  | $ 5,000,000 |  |  |  |  |  |  |
Convertible notes, Shares issued | shares |  |  |  | 120,476 |  |  |  |  |  |  |
Convertible debt conversion rate in shares of stock |  |  |  | 0.0239263 |  |  |  |  |  |  |
Conversion price of convertible notes | $ / shares |  |  |  |  |  |  |  |  |  | $ 41.795 |
Ladish Series B 6.14% Notes due 2016 [Member] |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |
Debt instrument carrying amount | [2] |  |  |  |  | $ 0 |  | $ 11,900,000 |  |  |
Debt instrument interest rate stated percentage | [2] |  |  |  |  | 6.14% |  | 6.14% |  |  |
Repayments of Debt |  |  |  |  |  | $ 5,700,000 |  |  |  |  |
Ladish Series C 6.41% Notes due 2015 [Member] |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |
Debt instrument carrying amount | [3] |  |  |  |  | $ 0 |  | $ 10,300,000 |  |  |
Debt instrument interest rate stated percentage | [3] |  |  |  |  | 6.41% |  | 6.41% |  |  |
Repayments of Debt |  |  |  |  |  | $ 10,000,000 |  |  |  |  |
Domestic Bank Group $400 million unsecured credit agreement [Member] |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |
Debt instrument carrying amount |  |  |  |  |  |  |  | $ 0 |  |  |
Seperate Letter of Credit Facility [Member] |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |
Line of credit facility amount outstanding |  |  |  |  |  | $ 32,000,000 |  |  |  |  |
STAL Revolving Credit Facility [Member] |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |
Joint venture ownership percentage |  |  |  |  |  | 60.00% |  |  |  |  |
Maximum [Member] | Allegheny Technologies $500 million 5.875% Senior Notes due 2023 [Member] |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |
Debt instrument interest rate stated percentage |  |  |  |  |  | 7.875% |  |  |  |  |
Domestic Bank Group $400 million credit agreement [Member] |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |
Line of Credit Facility, Average Outstanding Amount |  |  |  |  |  | $ 61,000,000 |  |  |  |  |
Line of Credit Facility, Interest Rate During Period |  |  |  |  |  | 2.00% |  |  |  |  |
STAL Revolving Credit Facility [Member] |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |
Line of credit maximum borrowing capacity |  |  |  |  |  | $ 20,000,000 |  |  |  |  |
Allegheny Technologies, Senior Notes, 5.875, Due 2023 [Member] |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |
Increase in stated interest rate due to downgrade (percent) |  |  |  |  |  | 1.75% |  |  |  |  |
Additional Annual Interest Expense to be Incurred |  |  |  |  |  | $ 4,100,000 |  |  |  |  |
Credit Downgrade, Increase in Interest Expense per Downgrade Notch, Percent |  |  |  |  |  | 0.25% |  |  |  |  |
Credit Downgrade, Maximum Number of Downgrade Notches |  |  |  |  |  | 4 |  |  |  |  |
Credit Downgrade, Maximum Increase in Interest Rate Expense, Percent |  |  |  |  |  | 2.00% |  |  |  |  |
Domestic Bank Group $400 million asset-based credit facility [Member] |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |
Debt instrument carrying amount |  |  |  |  |  | $ 0 |  |  |  |  |
Line of credit facility amount outstanding |  |  |  |  |  | $ 4,600,000 |  |  |  |  |
Revolving Credit Facility [Member] | Domestic Bank Group $400 million credit agreement [Member] |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |
Line of credit maximum borrowing capacity |  |  |  |  |  |  |  | $ 400,000,000 |  |  |
Revolving Credit Facility [Member] | Domestic Bank Group $400 million asset-based credit facility [Member] |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |
Amortization period of debt issuance costs |  | 5 years |  |  |  |  |  |  |  |  |
Line of credit maximum borrowing capacity |  | $ 400,000,000 |  |  |  |  |  |  |  |  |
Debt Issuance Cost |  | 1,500,000 |  |  |  |  |  |  |  |  |
Debt Instrument, Covenant, Remaining Borrowing Capacity |  | 40,000,000 |  |  |  |  |  |  |  |  |
Debt Instrument, Covenant, Minimum Required Liquidity |  | $ 500,000,000 |  |  |  |  |  |  |  |  |
Debt Instrument, Covenant, Minimum Liquidity, Number of Days Prior |  | 91 days |  |  |  |  |  |  |  |  |
Debt Instrument, Covenant, Fixed Charge Coverage Ratio |  | 1 |  |  |  |  |  |  |  |  |
Debt Instrument, Covenant, Remaining Borrowing Capacity, Percent Minimum Borrowing Capacity |  | 10.00% |  |  |  |  |  |  |  |  |
Revolving Credit Facility [Member] | Domestic Bank Group $400 million asset-based credit facility [Member] | Minimum [Member] | London Interbank Offered Rate (LIBOR) [Member] |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |
Variable rate spread |  | 1.25% |  |  |  |  |  |  |  |  |
Revolving Credit Facility [Member] | Domestic Bank Group $400 million asset-based credit facility [Member] | Minimum [Member] | Base Rate [Member] |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |
Variable rate spread |  | 0.25% |  |  |  |  |  |  |  |  |
Revolving Credit Facility [Member] | Domestic Bank Group $400 million asset-based credit facility [Member] | Maximum [Member] | London Interbank Offered Rate (LIBOR) [Member] |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |
Variable rate spread |  | 1.75% |  |  |  |  |  |  |  |  |
Revolving Credit Facility [Member] | Domestic Bank Group $400 million asset-based credit facility [Member] | Maximum [Member] | Base Rate [Member] |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |
Variable rate spread |  | 0.75% |  |  |  |  |  |  |  |  |
Letter of Credit [Member] | Domestic Bank Group $400 million asset-based credit facility [Member] |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |
Line of credit maximum borrowing capacity |  | $ 200,000,000 |  |  |  |  |  |  |  |  |
[1] | Bearing interest at 7.625% effective August 15, 2015.
[2] | Includes fair value adjustment of $0.4 million at December 31, 2014.
[3] | Includes fair value adjustment of $0.3 million at December 31, 2014.

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- Definition The value of the financial instrument(s) that the original debt is being converted into in a noncash (or part noncash) transaction. "Part noncash" refers to that portion of the transaction not resulting in cash receipts or cash payments in the period. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 230 -SubTopic 10 -Section 50 -Paragraph 3 -URI http://asc.fasb.org/extlink&oid=6367179&loc=d3e4304-108586 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 230 -SubTopic 10 -Section 50 -Paragraph 5 -URI http://asc.fasb.org/extlink&oid=6367179&loc=d3e4332-108586 + Details
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- Definition Amount of long-term debt before deduction of unamortized discount or premium. Includes, but is not limited to, notes payable, bonds payable, commercial loans, mortgage loans, convertible debt, subordinated debt and other types of debt, with initial maturities beyond one year or the normal operating cycle, if longer. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02.22) -URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 02 -Paragraph 20 -Article 5 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 03 -Paragraph 16 -Article 9 + Details
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- Definition Period of time between issuance and maturity of debt instrument, in PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days. + References No definition available. + Details
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- Definition The carrying value as of the balance sheet date of the current and noncurrent portions of long-term obligations drawn from a line of credit, which is a bank's commitment to make loans up to a specific amount. Examples of items that might be included in the application of this element may consist of letters of credit, standby letters of credit, and revolving credit arrangements, under which borrowings can be made up to a maximum amount as of any point in time conditional on satisfaction of specified terms before, as of and after the date of drawdowns on the line. Includes short-term obligations that would normally be classified as current liabilities but for which (a) postbalance sheet date issuance of a long term obligation to refinance the short term obligation on a long term basis, or (b) the enterprise has entered into a financing agreement that clearly permits the enterprise to refinance the short-term obligation on a long term basis and the following conditions are met (1) the agreement does not expire within 1 year and is not cancelable by the lender except for violation of an objectively determinable provision, (2) no violation exists at the BS date, and (3) the lender has entered into the financing agreement is expected to be financially capable of honoring the agreement. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 942 -SubTopic 210 -Section S99 -Paragraph 1 -Subparagraph (SX 210.9-03.16) -URI http://asc.fasb.org/extlink&oid=6876686&loc=d3e534808-122878 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 944 -SubTopic 210 -Section S99 -Paragraph 1 -Subparagraph (SX 210.7-03.16) -URI http://asc.fasb.org/extlink&oid=6879938&loc=d3e572229-122910 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 02 -Paragraph 19, 20, 22 -Article 5 + Details
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- Definition Average amount borrowed under the credit facility during the period. + References No definition available. + Details
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- Definition The effective interest rate during the reporting period. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02.19(b),22(b)) -URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682 + Details
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- Definition Maximum borrowing capacity under the credit facility without consideration of any current restrictions on the amount that could be borrowed or the amounts currently outstanding under the facility. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02.19(b),22(b)) -URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682 + Details
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- Definition Amount of long-term debt payable, sinking fund requirements, and other securities issued that are redeemable by holder at fixed or determinable prices and dates maturing in the next fiscal year following the latest fiscal year. Excludes interim and annual periods when interim periods are reported on a rolling approach, from latest balance sheet date. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 235 -SubTopic 10 -Section S99 -Paragraph 3 -Subparagraph (SX 210.12-04.(a)) -URI http://asc.fasb.org/extlink&oid=26873400&loc=d3e24072-122690 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 470 -SubTopic 10 -Section 50 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=6802200&loc=d3e1835-112601 + Details
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- Definition Amount of long-term debt payable, sinking fund requirements, and other securities issued that are redeemable by holder at fixed or determinable prices and dates maturing in the fifth fiscal year following the latest fiscal year. Excludes interim and annual periods when interim periods are reported on a rolling approach, from latest balance sheet date. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 470 -SubTopic 10 -Section 50 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=6802200&loc=d3e1835-112601 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 235 -SubTopic 10 -Section S99 -Paragraph 3 -Subparagraph (SX 210.12-04.(a)) -URI http://asc.fasb.org/extlink&oid=26873400&loc=d3e24072-122690 + Details
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- Definition Amount of long-term debt payable, sinking fund requirements, and other securities issued that are redeemable by holder at fixed or determinable prices and dates maturing in the third fiscal year following the latest fiscal year. Excludes interim and annual periods when interim periods are reported on a rolling approach, from latest balance sheet date. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 470 -SubTopic 10 -Section 50 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=6802200&loc=d3e1835-112601 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 235 -SubTopic 10 -Section S99 -Paragraph 3 -Subparagraph (SX 210.12-04.(a)) -URI http://asc.fasb.org/extlink&oid=26873400&loc=d3e24072-122690 + Details
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- Definition Amount of long-term debt payable, sinking fund requirements, and other securities issued that are redeemable by holder at fixed or determinable prices and dates maturing in the second fiscal year following the latest fiscal year. Excludes interim and annual periods when interim periods are reported on a rolling approach, from latest balance sheet date. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 470 -SubTopic 10 -Section 50 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=6802200&loc=d3e1835-112601 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 235 -SubTopic 10 -Section S99 -Paragraph 3 -Subparagraph (SX 210.12-04.(a)) -URI http://asc.fasb.org/extlink&oid=26873400&loc=d3e24072-122690 + Details
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- Definition The cash outflow paid to third parties in connection with debt origination, which will be amortized over the remaining maturity period of the associated long-term debt. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 230 -SubTopic 10 -Section 45 -Paragraph 15 -Subparagraph (e) -URI http://asc.fasb.org/extlink&oid=56944662&loc=d3e3291-108585 + Details
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