Income Taxes	9 Months Ended
Sep. 30, 2016
Income Tax Disclosure [Abstract]
Income Taxes	O. Income Taxes – The effective tax rate for the third quarter of 2016 and 2015 was 86.8% (provision on income) and 550.0% (provision on income), respectively. The rate for the 2016 third quarter differs from the U.S. federal statutory rate of 35% primarily due to U.S. losses and tax credits with no tax benefit realizable by Alcoa Corporation, somewhat offset by foreign income taxed in lower rate jurisdictions and tax benefits on interest expense eliminated to Parent Company net investment. The rate for the 2015 third quarter differs from the U.S. federal statutory rate of 35% primarily due to U.S. losses and tax credits with no tax benefit realizable by Alcoa Corporation. The effective tax rate for the 2016 and 2015 nine-month periods was 712.0% (provision on a loss) and 67.2% (provision on income), respectively. The rate for the 2016 nine-month period differs (by (747.0) percentage points) from the U.S. federal statutory rate of 35% primarily due to U.S. losses and tax credits with no tax benefit realizable by Alcoa Corporation, slightly offset by foreign income taxed in lower rate jurisdictions and tax benefits on interest expense eliminated to Parent Company net investment. The rate for the 2015 nine-month period differs from the U.S. federal statutory rate of 35% primarily due to an $85 discrete income tax charge ($51 after noncontrolling interest) for a valuation allowance on certain deferred tax assets in Suriname, which were mostly related to employee benefits and tax loss carryforwards, and U.S. losses and tax credits with no tax benefit realizable by Alcoa Corporation.

Income Taxes

9 Months Ended

Sep. 30, 2016

O. Income Taxes – The effective tax rate for the third quarter of 2016 and 2015 was 86.8% (provision on income) and 550.0% (provision on income), respectively.

The rate for the 2016 third quarter differs from the U.S. federal statutory rate of 35% primarily due to U.S. losses and tax credits with no tax benefit realizable by Alcoa Corporation, somewhat offset by foreign income taxed in lower rate jurisdictions and tax benefits on interest expense eliminated to Parent Company net investment.

The rate for the 2015 third quarter differs from the U.S. federal statutory rate of 35% primarily due to U.S. losses and tax credits with no tax benefit realizable by Alcoa Corporation.

The effective tax rate for the 2016 and 2015 nine-month periods was 712.0% (provision on a loss) and 67.2% (provision on income), respectively.

The rate for the 2016 nine-month period differs (by (747.0) percentage points) from the U.S. federal statutory rate of 35% primarily due to U.S. losses and tax credits with no tax benefit realizable by Alcoa Corporation, slightly offset by foreign income taxed in lower rate jurisdictions and tax benefits on interest expense eliminated to Parent Company net investment.

The rate for the 2015 nine-month period differs from the U.S. federal statutory rate of 35% primarily due to an $85 discrete income tax charge ($51 after noncontrolling interest) for a valuation allowance on certain deferred tax assets in Suriname, which were mostly related to employee benefits and tax loss carryforwards, and U.S. losses and tax credits with no tax benefit realizable by Alcoa Corporation.