Commitments and contingencies	12 Months Ended
Dec. 31, 2015
Commitments and Contingencies Disclosure [Abstract]
Commitments and contingencies	Commitments and contingencies Environmental Contingencies Based upon all available information, we believe our current environmental liabilities do not have, and are not likely to have, a material adverse effect on our financial condition, results of operations or liquidity. Because of the issues and uncertainties described below and the inability to predict the requirements of future environmental laws, there can be no assurance that future capital expenditures and costs for environmental compliance at currently or formerly owned or operated properties will not result in liabilities that may have a material adverse effect on our financial condition, results of operations or liquidity. We accrue for costs associated with environmental assessments and remedial efforts when it becomes probable that a liability has been incurred and the costs can be reasonably estimated. The aggregate environmental-related accrued liabilities were $1,112 and $1,101 at December 31, 2015 and 2014, respectively. All accrued amounts have been recorded without giving effect to any possible future recoveries. With respect to costs for ongoing environmental compliance, including maintenance and monitoring, such costs are expensed as incurred. In July 2006, we were named as a defendant, together with certain affiliates of Alcan Inc., in a lawsuit brought by Alcoa Inc. seeking to determine responsibility for certain environmental indemnity obligations related to the sale of a cast aluminum plate manufacturing facility located in Vernon, California, which we purchased from Alcoa Inc. in December 1998, and sold to Alcan Rolled Products-Ravenswood LLC in July 1999. The complaint also seeks costs and attorney fees. The matter is in a preliminary stage in the U.S. District Court for the District of Delaware, and we cannot predict the ultimate outcome of this action or estimate a range of possible losses related to this matter at this time. Matters relating to the St. Croix Alumina Refining Facility We are a party to a United States Environmental Protection Agency Administrative Order on Consent (the "Order") pursuant to which certain past and present owners of an alumina refining facility at St. Croix, Virgin Islands (the "St. Croix Alumina Refinery") have agreed to carry out a Hydrocarbon Recovery Plan to remove and manage hydrocarbons floating on groundwater underlying the facility. Pursuant to the Hydrocarbon Recovery Plan, recovered hydrocarbons and groundwater are delivered to the adjacent petroleum refinery where they are received and managed. In connection with the sale of the facility by Lockheed Martin Corporation ("Lockheed") to one of our affiliates, Virgin Islands Alumina Corporation ("Vialco"), in 1989, Lockheed, Vialco and Century entered into the Lockheed-Vialco Asset Purchase Agreement. The indemnity provisions contained in the Lockheed-Vialco Asset Purchase Agreement allocate responsibility for certain environmental matters. Lockheed has tendered indemnity to Vialco. We have likewise tendered indemnity to Lockheed. Through December 31, 2015, we have expended approximately $1,085 on the Hydrocarbon Recovery Plan. At this time, we are not able to estimate the amount of any future potential payments under this indemnification to comply with the Order, but we do not anticipate that any such amounts will have a material adverse effect on our financial condition, results of operations or liquidity, regardless of the final outcome. Vialco sold the St. Croix Alumina Refinery to St. Croix Alumina, LLC, a subsidiary of Alcoa, in 1995. In December 2010, Century was among several defendants named in a lawsuit filed by plaintiffs who either worked, resided or owned property in the area downwind from the St. Croix Alumina Refinery. In March 2011, Century was also named a defendant in a nearly identical suit brought by certain additional plaintiffs. The plaintiffs in both suits allege damages caused by the presence of red mud and other particulates coming from the alumina facility and are seeking unspecified monetary damages, costs and attorney fees as well as certain injunctive relief. We have tendered indemnity and defense to St. Croix Alumina LLC and Alcoa Alumina & Chemical LLC under the terms of an acquisition agreement relating to the facility and have filed motions to dismiss plaintiffs’ claims. In August 2015, the Superior Court of the Virgin Islands, Division of St. Croix denied the motions to dismiss but ordered all plaintiffs to refile individual complaints. At this time, we are not able to predict the ultimate outcome of or to estimate a range of possible losses for any of the foregoing actions relating to the St. Croix Alumina Refinery. Legal Contingencies In addition to the foregoing matters, we have pending against us or may be subject to various lawsuits, claims and proceedings related primarily to employment, commercial, stockholder, safety and health matters. In evaluating whether to accrue for losses associated with legal contingencies, it is our policy to take into consideration factors such as the facts and circumstances asserted, our historical experience with contingencies of a similar nature, the likelihood of our prevailing and the severity of any potential loss. For some matters, no accrual is established because we have assessed our risk of loss to be remote. Where the risk of loss is probable and the amount of the loss can be reasonably estimated, we record an accrual, either on an individual basis or with respect to a group of matters involving similar claims, based on the factors set forth above. When we have assessed that a loss associated with legal contingencies is reasonably possible, we determine if estimates of possible losses or ranges of possible losses are in excess of related accrued liabilities, if any. Based on current knowledge, management has ascertained estimates for losses that are reasonably possible and management does not believe that any reasonably possible outcomes in excess of our accruals, if any, either individually or in aggregate, would be material to our financial condition, results of operations, or liquidity. We reevaluate and update our assessments and accruals as matters progress over time. Ravenswood Retiree Medical Benefits changes In November 2009, CAWV filed a class action complaint for declaratory judgment against the United Steel, Paper and Forestry, Rubber, Manufacturing, Energy, Allied Industrial and Service Workers International Union (the "USW"), the USW’s local and certain CAWV retirees, individually and as class representatives, seeking a declaration of CAWV’s rights to modify/terminate retiree medical benefits. Later in November 2009, the USW and representatives of a retiree class filed a separate suit against CAWV, Century Aluminum Company, Century Aluminum Master Welfare Benefit Plan, and various John Does with respect to the foregoing. These actions, entitled Dewhurst, et al. v. Century Aluminum Co., et al., and Century Aluminum of West Virginia, Inc. v. United Steel, Paper and Forestry, Rubber, Manufacturing, Energy, Allied Industrial and Service Workers International Union, AFL-CIO/CLC, et al., have been consolidated and venue has been set in the District Court for the Southern District of West Virginia. In September 2015, the trial court granted CAWV's motion for summary judgment of these actions. The trial court decision is currently being appealed by the USW to the Court of Appeals for the 4th Circuit. PBGC Settlement In April 2013, we entered into a settlement agreement with the Pension Benefit Guaranty Corporation ("PBGC") regarding an alleged "cessation of operations" at our Ravenswood facility as a result of the curtailment of operations at the facility and, pursuant to the agreement, we agreed to make additional contributions (above any minimum required contributions) to our defined benefit pension plans totaling approximately $17,400 over the term of the agreement, which runs through 2016. Under certain circumstances, in periods of lower primary aluminum prices relative to our cost of operations, we may defer one or more of these payments, but we would be required to provide the PBGC with acceptable security for any deferred payments. We made the contributions pursuant to this agreement of $1,100 in 2015 and $6,700 in 2013. We did not make any contribution during 2014. The remaining contributions under this agreement are approximately $9,600. Power Commitments and Contingencies Hawesville CAKY is party to a power supply arrangement with Kenergy and Big Rivers which provides market-based power to the Hawesville smelter. The power supply arrangement has an effective term through December 2023. Under this arrangement, the power companies purchase power on the open market and pass it through to Hawesville at Midcontinent Independent System Operator ("MISO") pricing plus transmission and other costs incurred by Kenergy. Effective January 1, 2015, new agreements were approved by the Kentucky Public Service Commission pursuant to which EDF Trading North America, LLC ("EDF") replaced Big Rivers as the market participant with MISO under this arrangement. Sebree Century Sebree is party to a power supply arrangement with Kenergy and Big Rivers which provides market-based power to the Sebree smelter. The power supply arrangement has an effective term through December 2023. Similar to the arrangement at Hawesville, the power companies purchase power on the open market and pass it through to Sebree at MISO pricing plus transmission and other costs incurred by Kenergy. Effective January 1, 2015, new agreements were approved by the Kentucky Public Service Commission pursuant to which EDF replaced Big Rivers as our market participant with MISO under this arrangement. Mt. Holly CASC's power agreement with the South Carolina Public Service Authority ("Santee Cooper") for power to the Mt. Holly smelter expired on December 31, 2015. On December 18, 2015, CASC reached an agreement with Santee Cooper that would allow Mt. Holly to operate at 50% capacity while CASC worked on a long-term solution that would allow Mt. Holly to access market power for all our its power supply requirements. This agreement with Santee Cooper provides for the supply of power to Mt. Holly from two sources: (1) 25% of the Mt. Holly load is served from Santee Cooper’s generation at a standard cost-based industrial rate and (2) 75% of the power to serve Mt. Holly is sourced from a third party supplier from generation that is outside Santee Cooper’s service territory at market prices plus transmission that are tied to natural gas prices. The agreement with Santee Cooper has a term through December 31, 2018 but can be terminated by Mt. Holly on 60 days' notice; the current third party supply contract has a term through May 31, 2016. Grundartangi Nordural Grundartangi ehf has power purchase agreements with HS Orka hf ("HS"), Landsvirkjun and Orkuveita Reykjavikur ("OR") to provide power to its Grundartangi smelter. These power purchase agreements, which will expire on various dates from 2019 through 2036 (subject to extension), provide power at LME-based variable rates. Each power purchase agreement contains take-or-pay obligations with respect to a significant percentage of the total committed and available power under such agreement. In June 2012, Nordural Grundartangi ehf entered into a supplemental power contract with Landsvirkjun. The supplemental power contract, which will expire in October 2029 (or upon the occurrence of certain earlier events), will provide Nordural Grundartangi ehf with supplemental power, as Nordural Grundartangi ehf may request from time to time, at LME-based variable rates. Nordural Grundartangi ehf made certain prepayments to Landsvirkjun for power expected to be used at a later date in connection with the contract, which will reduce the price paid for power at the time of consumption. As of December 31, 2015, these power prepayments totaled approximately $1,477. Helguvik Nordural Helguvik ehf has power purchase agreements with HS and OR to provide power to the Helguvik project. These power purchase agreements provide power at LME-based variable rates and contain take-or-pay obligations with respect to a significant percentage of the total committed and available power under such agreements. The power purchase agreements with HS and OR to provide power to Helguvik contain certain conditions to HS’s and OR’s obligations. HS (with respect to all phases) and OR (with respect to all phases other than the first phase) have alleged that certain of these conditions have not been satisfied. The first stage of power under the OR power purchase agreement (approximately 47.5 MW) became available in the fourth quarter of 2011 and is currently being utilized at Grundartangi. In July 2014, HS commenced arbitration proceedings against Nordural Helguvik ehf seeking, among other things, an order declaring, (i) that the conditions to the power contract have not been fulfilled and, (ii) that the power contract is therefore no longer valid. Nordural Helguvik ehf believes HS' claims are without merit and intends to defend itself against them. Nordural Helguvik ehf is in discussions with both HS and OR with respect to such conditions and other matters pertaining to these agreements. In June 2014, Nordural Helguvik ehf entered into a supplemental power contract with OR which will expire in October 2036 (or upon the occurrence of certain earlier events) and will provide Grundartangi or Helguvik with supplemental power at LME-based rates, as may be requested from Grundartangi or Helguvik from time to time. Other Commitments and Contingencies Labor Commitments The bargaining unit employees at our Grundartangi, Vlissingen, Hawesville, Sebree and Ravenswood facilities are represented by labor unions, representing 63% of our total workforce. 84% of Grundartangi’s work force is represented by five labor unions, governed by a labor agreement that establishes wages and work rules for covered employees. A new labor agreement was reached in 2015 which is effective through December 31, 2019. 100% of Vlissingen's work force is represented by the FME, governed by a labor agreement that expired on May 1, 2015 and contract negotiations are in process. The FME negotiates working conditions with trade unions on behalf of its members. 53% of our U.S. based work force is represented by USW. In June 2015, CAKY entered into a new collective bargaining agreement with the USW for its employees at the Hawesville smelter. The agreement is effective through April 1, 2020. Century Sebree has a collective bargaining agreement with the USW for its employees at the Sebree smelter that is effective through October 28, 2019. The labor agreement for CAWV’s Ravenswood plant employees represented by the USW expired on August 31, 2010.

Commitments and contingencies

Environmental Contingencies

Based upon all available information, we believe our current environmental liabilities do not have, and are not likely to have, a material adverse effect on our financial condition, results of operations or liquidity. Because of the issues and uncertainties described below and the inability to predict the requirements of future environmental laws, there can be no assurance that future capital expenditures and costs for environmental compliance at currently or formerly owned or operated properties will not result in liabilities that may have a material adverse effect on our financial condition, results of operations or liquidity.

We accrue for costs associated with environmental assessments and remedial efforts when it becomes probable that a liability has been incurred and the costs can be reasonably estimated. The aggregate environmental-related accrued liabilities were $1,112 and $1,101 at December 31, 2015 and 2014, respectively. All accrued amounts have been recorded without giving effect to any possible future recoveries. With respect to costs for ongoing environmental compliance, including maintenance and monitoring, such costs are expensed as incurred.

In July 2006, we were named as a defendant, together with certain affiliates of Alcan Inc., in a lawsuit brought by Alcoa Inc. seeking to determine responsibility for certain environmental indemnity obligations related to the sale of a cast aluminum plate manufacturing facility located in Vernon, California, which we purchased from Alcoa Inc. in December 1998, and sold to Alcan Rolled Products-Ravenswood LLC in July 1999. The complaint also seeks costs and attorney fees. The matter is in a preliminary stage in the U.S. District Court for the District of Delaware, and we cannot predict the ultimate outcome of this action or estimate a range of possible losses related to this matter at this time.

Matters relating to the St. Croix Alumina Refining Facility

We are a party to a United States Environmental Protection Agency Administrative Order on Consent (the "Order") pursuant to which certain past and present owners of an alumina refining facility at St. Croix, Virgin Islands (the "St. Croix Alumina Refinery") have agreed to carry out a Hydrocarbon Recovery Plan to remove and manage hydrocarbons floating on groundwater underlying the facility. Pursuant to the Hydrocarbon Recovery Plan, recovered hydrocarbons and groundwater are delivered to the adjacent petroleum refinery where they are received and managed. In connection with the sale of the facility by Lockheed Martin Corporation ("Lockheed") to one of our affiliates, Virgin Islands Alumina Corporation ("Vialco"), in 1989, Lockheed, Vialco and Century entered into the Lockheed-Vialco Asset Purchase Agreement. The indemnity provisions contained in the Lockheed-Vialco Asset Purchase Agreement allocate responsibility for certain environmental matters. Lockheed has tendered indemnity to Vialco. We have likewise tendered indemnity to Lockheed. Through December 31, 2015, we have expended approximately $1,085 on the Hydrocarbon Recovery Plan. At this time, we are not able to estimate the amount of any future potential payments under this indemnification to comply with the Order, but we do not anticipate that any such amounts will have a material adverse effect on our financial condition, results of operations or liquidity, regardless of the final outcome. Vialco sold the St. Croix Alumina Refinery to St. Croix Alumina, LLC, a subsidiary of Alcoa, in 1995.

In December 2010, Century was among several defendants named in a lawsuit filed by plaintiffs who either worked, resided or owned property in the area downwind from the St. Croix Alumina Refinery. In March 2011, Century was also named a defendant in a nearly identical suit brought by certain additional plaintiffs. The plaintiffs in both suits allege damages caused by the presence of red mud and other particulates coming from the alumina facility and are seeking unspecified monetary damages, costs and attorney fees as well as certain injunctive relief. We have tendered indemnity and defense to St. Croix Alumina LLC and Alcoa Alumina & Chemical LLC under the terms of an acquisition agreement relating to the facility and have filed motions to dismiss plaintiffs’ claims. In August 2015, the Superior Court of the Virgin Islands, Division of St. Croix denied the motions to dismiss but ordered all plaintiffs to refile individual complaints. At this time, we are not able to predict the ultimate outcome of or to estimate a range of possible losses for any of the foregoing actions relating to the St. Croix Alumina Refinery.

Legal Contingencies

In addition to the foregoing matters, we have pending against us or may be subject to various lawsuits, claims and proceedings related primarily to employment, commercial, stockholder, safety and health matters.

In evaluating whether to accrue for losses associated with legal contingencies, it is our policy to take into consideration factors such as the facts and circumstances asserted, our historical experience with contingencies of a similar nature, the likelihood of our prevailing and the severity of any potential loss. For some matters, no accrual is established because we have assessed our risk of loss to be remote. Where the risk of loss is probable and the amount of the loss can be reasonably estimated, we record an accrual, either on an individual basis or with respect to a group of matters involving similar claims, based on the factors set forth above.

When we have assessed that a loss associated with legal contingencies is reasonably possible, we determine if estimates of possible losses or ranges of possible losses are in excess of related accrued liabilities, if any. Based on current knowledge, management has ascertained estimates for losses that are reasonably possible and management does not believe that any reasonably possible outcomes in excess of our accruals, if any, either individually or in aggregate, would be material to our financial condition, results of operations, or liquidity. We reevaluate and update our assessments and accruals as matters progress over time.

Ravenswood Retiree Medical Benefits changes

In November 2009, CAWV filed a class action complaint for declaratory judgment against the United Steel, Paper and Forestry, Rubber, Manufacturing, Energy, Allied Industrial and Service Workers International Union (the "USW"), the USW’s local and certain CAWV retirees, individually and as class representatives, seeking a declaration of CAWV’s rights to modify/terminate retiree medical benefits. Later in November 2009, the USW and representatives of a retiree class filed a separate suit against CAWV, Century Aluminum Company, Century Aluminum Master Welfare Benefit Plan, and various John Does with respect to the foregoing. These actions, entitled Dewhurst, et al. v. Century Aluminum Co., et al., and Century Aluminum of West Virginia, Inc. v. United Steel, Paper and Forestry, Rubber, Manufacturing, Energy, Allied Industrial and Service Workers International Union, AFL-CIO/CLC, et al., have been consolidated and venue has been set in the District Court for the Southern District of West Virginia.

In September 2015, the trial court granted CAWV's motion for summary judgment of these actions. The trial court decision is currently being appealed by the USW to the Court of Appeals for the 4th Circuit.

PBGC Settlement

In April 2013, we entered into a settlement agreement with the Pension Benefit Guaranty Corporation ("PBGC") regarding an alleged "cessation of operations" at our Ravenswood facility as a result of the curtailment of operations at the facility and, pursuant to the agreement, we agreed to make additional contributions (above any minimum required contributions) to our defined benefit pension plans totaling approximately $17,400 over the term of the agreement, which runs through 2016. Under certain circumstances, in periods of lower primary aluminum prices relative to our cost of operations, we may defer one or more of these payments, but we would be required to provide the PBGC with acceptable security for any deferred payments. We made the contributions pursuant to this agreement of $1,100 in 2015 and $6,700 in 2013. We did not make any contribution during 2014. The remaining contributions under this agreement are approximately $9,600.

Power Commitments and Contingencies

Hawesville

CAKY is party to a power supply arrangement with Kenergy and Big Rivers which provides market-based power to the Hawesville smelter. The power supply arrangement has an effective term through December 2023. Under this arrangement, the power companies purchase power on the open market and pass it through to Hawesville at Midcontinent Independent System Operator ("MISO") pricing plus transmission and other costs incurred by Kenergy. Effective January 1, 2015, new agreements were approved by the Kentucky Public Service Commission pursuant to which EDF Trading North America, LLC ("EDF") replaced Big Rivers as the market participant with MISO under this arrangement.

Sebree

Century Sebree is party to a power supply arrangement with Kenergy and Big Rivers which provides market-based power to the Sebree smelter. The power supply arrangement has an effective term through December 2023. Similar to the arrangement at Hawesville, the power companies purchase power on the open market and pass it through to Sebree at MISO pricing plus transmission and other costs incurred by Kenergy. Effective January 1, 2015, new agreements were approved by the Kentucky Public Service Commission pursuant to which EDF replaced Big Rivers as our market participant with MISO under this arrangement.

Mt. Holly

CASC's power agreement with the South Carolina Public Service Authority ("Santee Cooper") for power to the Mt. Holly smelter expired on December 31, 2015. On December 18, 2015, CASC reached an agreement with Santee Cooper that would allow Mt. Holly to operate at 50% capacity while CASC worked on a long-term solution that would allow Mt. Holly to access market power for all our its power supply requirements. This agreement with Santee Cooper provides for the supply of power to Mt. Holly from two sources: (1) 25% of the Mt. Holly load is served from Santee Cooper’s generation at a standard cost-based industrial rate and (2) 75% of the power to serve Mt. Holly is sourced from a third party supplier from generation that is outside Santee Cooper’s service territory at market prices plus transmission that are tied to natural gas prices. The agreement with Santee Cooper has a term through December 31, 2018 but can be terminated by Mt. Holly on 60 days' notice; the current third party supply contract has a term through May 31, 2016.

Grundartangi

Nordural Grundartangi ehf has power purchase agreements with HS Orka hf ("HS"), Landsvirkjun and Orkuveita Reykjavikur ("OR") to provide power to its Grundartangi smelter. These power purchase agreements, which will expire on various dates from 2019 through 2036 (subject to extension), provide power at LME-based variable rates. Each power purchase agreement contains take-or-pay obligations with respect to a significant percentage of the total committed and available power under such agreement.

In June 2012, Nordural Grundartangi ehf entered into a supplemental power contract with Landsvirkjun. The supplemental power contract, which will expire in October 2029 (or upon the occurrence of certain earlier events), will provide Nordural Grundartangi ehf with supplemental power, as Nordural Grundartangi ehf may request from time to time, at LME-based variable rates. Nordural Grundartangi ehf made certain prepayments to Landsvirkjun for power expected to be used at a later date in connection with the contract, which will reduce the price paid for power at the time of consumption. As of December 31, 2015, these power prepayments totaled approximately $1,477.

Helguvik

Nordural Helguvik ehf has power purchase agreements with HS and OR to provide power to the Helguvik project. These power purchase agreements provide power at LME-based variable rates and contain take-or-pay obligations with respect to a significant percentage of the total committed and available power under such agreements. The power purchase agreements with HS and OR to provide power to Helguvik contain certain conditions to HS’s and OR’s obligations. HS (with respect to all phases) and OR (with respect to all phases other than the first phase) have alleged that certain of these conditions have not been satisfied. The first stage of power under the OR power purchase agreement (approximately 47.5 MW) became available in the fourth quarter of 2011 and is currently being utilized at Grundartangi. In July 2014, HS commenced arbitration proceedings against Nordural Helguvik ehf seeking, among other things, an order declaring, (i) that the conditions to the power contract have not been fulfilled and, (ii) that the power contract is therefore no longer valid. Nordural Helguvik ehf believes HS' claims are without merit and intends to defend itself against them. Nordural Helguvik ehf is in discussions with both HS and OR with respect to such conditions and other matters pertaining to these agreements.

In June 2014, Nordural Helguvik ehf entered into a supplemental power contract with OR which will expire in October 2036 (or upon the occurrence of certain earlier events) and will provide Grundartangi or Helguvik with supplemental power at LME-based rates, as may be requested from Grundartangi or Helguvik from time to time.

Other Commitments and Contingencies

Labor Commitments

The bargaining unit employees at our Grundartangi, Vlissingen, Hawesville, Sebree and Ravenswood facilities are represented by labor unions, representing 63% of our total workforce.

84% of Grundartangi’s work force is represented by five labor unions, governed by a labor agreement that establishes wages and work rules for covered employees. A new labor agreement was reached in 2015 which is effective through December 31, 2019. 100% of Vlissingen's work force is represented by the FME, governed by a labor agreement that expired on May 1, 2015 and contract negotiations are in process. The FME negotiates working conditions with trade unions on behalf of its members.

53% of our U.S. based work force is represented by USW. In June 2015, CAKY entered into a new collective bargaining agreement with the USW for its employees at the Hawesville smelter. The agreement is effective through April 1, 2020. Century Sebree has a collective bargaining agreement with the USW for its employees at the Sebree smelter that is effective through October 28, 2019. The labor agreement for CAWV’s Ravenswood plant employees represented by the USW expired on August 31, 2010.