Rate And Regulatory Matters	6 Months Ended
Jun. 30, 2015
Public Utilities, General Disclosures [Abstract]
RATE AND REGULATORY MATTERS	RATE AND REGULATORY MATTERS Below is a summary of updates to significant regulatory proceedings and related lawsuits. See also Note 2 - Rate and Regulatory Matters under Part II, Item 8, of the Form 10-K. We are unable to predict the ultimate outcome of these matters, the timing of the final decisions of the various agencies and courts, or the impact on our results of operations, financial position, or liquidity. Missouri 2015 Electric Rate Order In April 2015, the MoPSC issued an order approving an increase in Ameren Missouri’s annual revenues for electric service of $122 million, including $109 million related to the increase in net energy costs above those included in base rates previously authorized by the MoPSC. The remaining increase of $13 million approved by the order was for non-energy costs. The revenue increase was based on a 9.53% return on common equity, a capital structure composed of 51.8% common equity, and a rate base of $7.0 billion to reflect investments through December 31, 2014. Rate changes consistent with the order became effective on May 30, 2015. The order approved Ameren Missouri’s request for continued use of the FAC; however, it changed the FAC to exclude all transmission revenues and substantially all transmission charges. In addition, the order did not approve the continued use of the regulatory tracking mechanisms for storm costs and vegetation management and infrastructure inspection costs. These changes to Ameren Missouri’s recovery mechanisms are expected to contribute to regulatory lag. The order did approve the continued use of the regulatory tracking mechanisms for pension and other postretirement benefits, renewable energy standard costs, solar rebates, and uncertain tax positions that the MoPSC authorized in earlier electric rate orders. In addition, the order approved a reduction to Noranda’s electric rates with an offsetting increase in electric rates for Ameren Missouri’s other customers. The rate shift is revenue neutral to Ameren Missouri. In June 2015, Ameren Missouri filed a notice of appeal with the Missouri Court of Appeals, Western District, reserving the right to appeal the exclusion of all transmission revenues and substantially all transmission charges from the FAC, the reduction to Noranda’s electric rates, and the level of Noranda’s sales volume included in the MoPSC’s order. MEEIA Filing The MEEIA established a regulatory framework that, among other things, requires the MoPSC to ensure that a utility’s financial incentives are aligned to help customers use energy more efficiently, to provide timely cost recovery, and to provide earnings opportunities associated with cost effective energy efficiency programs. Missouri does not have a law mandating energy efficiency standards. In August 2012, the MoPSC approved Ameren Missouri’s customer energy efficiency programs, net shared benefits, and performance incentive for 2013 through 2015. The 2013 through 2015 plan anticipated Ameren Missouri would invest up to $147 million in customer energy efficiency programs, realize $100 million of net shared benefits, and be eligible for a performance incentive that would allow Ameren Missouri the potential to earn additional revenues by achieving certain customer energy efficiency goals, including $19 million if 100% of the goals are achieved during the three-year period. From January 2013 through June 2015, Ameren Missouri invested $95 million in customer energy efficiency programs and realized $115 million of net shared benefits. Ameren Missouri has not recorded revenues associated with the performance incentive, but does expect to exceed 100% of the customer energy efficiency goals by the end of 2015, subject to MoPSC review, and therefore expects to recognize revenues in excess of $19 million within the next two years. In December 2014, Ameren Missouri filed a three-year energy efficiency plan with the MoPSC under the MEEIA for 2016 to 2018 that included a portfolio of customer energy efficiency programs along with a rider to collect the program costs, net shared benefits, and a performance incentive from customers. Ameren Missouri amended this proposed plan in June 2015 when it filed a non-unanimous stipulation and agreement with certain intervenor parties. If this plan is approved by the MoPSC, beginning in January 2016, Ameren Missouri intends to invest up to $197 million over three years in the proposed customer energy efficiency programs. Ameren Missouri requested continued use of a MEEIA rider, which allows Ameren Missouri to collect from, or refund to, customers any difference in the actual amounts incurred and the amounts collected from customers for the MEEIA program costs and net shared benefits. Ameren Missouri anticipates net shared benefits would be approximately $65 million during this three-year plan. In addition, similar to its existing MEEIA energy efficiency plan that ends in December 2015, Ameren Missouri requested a performance incentive that would allow it to potentially earn additional revenues by achieving certain customer energy efficiency goals, including $30 million if 100% of the goals are achieved during the three-year period. Ameren Missouri would need to achieve at least 70% of its customer energy efficiency goals before it earns a performance incentive. In July 2015, the MoPSC staff and certain intervenor parties filed a non-unanimous stipulation and agreement that is unacceptable to Ameren Missouri. Even if approved by the MoPSC, Ameren Missouri is not required to implement an energy efficiency plan. There is no date by which the MoPSC must act with respect to the proposed customer energy efficiency plan. Ameren Missouri cannot predict the level of investment, net shared benefits, or performance incentive that the MoPSC may approve, if any, or whether it will ultimately implement a customer energy efficiency plan for the three-year period beginning in January 2016. Noranda Contract Notification Ameren Missouri supplies electricity to Noranda’s aluminum smelter in southeast Missouri under a long-term power supply agreement. In May 2015, Ameren Missouri notified Noranda of its intent to terminate the agreement effective June 1, 2020. In order to remove Noranda from its service territory, Ameren Missouri would also be required to obtain approval from the MoPSC. Sales to Noranda represented 5% of Ameren Missouri’s total electric revenue in 2014. ATXI Transmission Projects In May 2015, the MoPSC granted ATXI a certificate of convenience and necessity for the seven mile portion of the Illinois Rivers project located in Missouri. In June 2015, ATXI made a filing with the MoPSC requesting a certificate of convenience and necessity for the Mark Twain project. The Mark Twain project is a MISO-approved 100-mile transmission line located in northeast Missouri. A decision is expected from the MoPSC in 2016. Illinois IEIMA Under the provisions of the IEIMA’s formula rate framework, which currently extends through 2019, Ameren Illinois’ electric delivery service rates are subject to an annual revenue requirement reconciliation to its actual costs.Throughout each year, Ameren Illinois records a regulatory asset or a regulatory liability and a corresponding increase or decrease to operating revenues for any differences between the revenue requirement reflected in customer rates for that year and its estimate of the probable increase or decrease in the revenue requirement expected to ultimately be approved by the ICC based on that year's actual costs incurred. As of June 30, 2015, Ameren Illinois had recorded regulatory assets of $24 million, $102 million, and $36 million, to reflect its expected 2015, 2014, and 2013 revenue requirement reconciliation adjustments, with interest, respectively. Ameren Illinois is collecting the 2013 revenue requirement reconciliation adjustment from customers during 2015. In April 2015, Ameren Illinois filed with the ICC its annual electric delivery service formula rate update to establish the revenue requirement used for 2016 customer rates. Pending ICC approval, and if approved as filed, Ameren Illinois’ update filing would result in a $110 million increase in Ameren Illinois’ electric delivery service revenue requirement, beginning in January 2016. This update reflects an increase to the annual formula rate based on 2014 actual costs and expected net plant additions for 2015, an increase to include the 2014 revenue requirement reconciliation adjustment, and a decrease for the conclusion of the 2013 revenue requirement reconciliation adjustment, which will be fully collected from customers in 2015. In July 2015, the ICC staff submitted its calculation of the revenue requirement included in Ameren Illinois’ update filing. The ICC staff recommended adjustments that would result in a $107 million increase in Ameren Illinois’ electric delivery service revenue requirement. An ICC decision on this April 2015 filing is expected by December 2015. 2015 Natural Gas Delivery Service Rate Case In January 2015, Ameren Illinois filed a request with the ICC seeking approval to increase its annual revenues for natural gas delivery service. In an attempt to reduce regulatory lag, Ameren Illinois used a 2016 future test year in this proceeding. Additionally, the request included a proposal to implement a volume balancing adjustment for residential and small nonresidential customers. The volume balancing adjustment would ensure that changes in natural gas sales volumes do not result in an over or under collection of natural gas revenues for these rate classes. This case includes a capital structure composed of 50% common equity and a rate base of $1.2 billion. In July 2015, Ameren Illinois, the ICC staff, and certain other intervenors filed a stipulation and agreement with the ICC that would result in rates that are based on a return on common equity of 9.6%. The agreement does not address all the positions with all of the parties in the case. Based on the terms in the agreement and the unresolved positions in the case, Ameren Illinois' request seeks an annual revenue increase of $45 million, which Ameren Illinois estimates is materially identical to the ICC staff’s recommendation. The ICC staff and other intervenors did not oppose the volume balancing adjustment. A decision by the ICC in this proceeding is required by December 2015, with new rates expected to be effective in January 2016. Ameren Illinois cannot predict the level of any delivery service rate changes the ICC may approve, whether the ICC will approve the volume balancing adjustment, or if the ICC will approve the agreement between Ameren Illinois, the ICC staff, and certain other intervenors. In addition, Ameren Illinois cannot predict whether any rate changes that may eventually be approved will be sufficient to enable Ameren Illinois to recover its costs and to earn a reasonable return on investments when the rate changes go into effect. 2013 Natural Gas Delivery Service Rate Order In December 2013, the ICC issued a rate order that approved an increase in Ameren Illinois’ revenues for natural gas delivery service based on a 9.1% return on common equity. In March 2014, Ameren Illinois filed with the Appellate Court of the Fourth District of Illinois an appeal of the allowed return on common equity included in the ICC's order. Ameren Illinois sought a 10.4% return on common equity in this rate case. In June 2015, the Appellate Court of the Fourth District upheld the ICC’s rate order. Ameren Illinois does not intend to pursue any further appeals. 2015 ICC Purchased Power Reconciliation In January 2015, the ICC issued an order that approved Ameren Illinois' reconciliation of revenues collected under its purchased power rider mechanism and Ameren Illinois' related cumulative power usage cost. In the first quarter of 2015, based on the January 2015 order, both Ameren and Ameren Illinois recorded a $15 million increase to electric revenues for the recovery of this cumulative power usage cost from electric customers. ATXI Transmission Project In July 2015, Illinois administrative law judges issued a proposed order that recommended a certificate of public convenience and necessity and project approval for the Spoon River project. The Spoon River project is a MISO-approved 35-mile transmission line to be constructed in northwest Illinois. A final order from the ICC is expected in 2015. A certificate of public convenience and necessity is required before ATXI can proceed with right-of-way acquisition. Federal Ameren Illinois Electric Transmission Rate Refund In July 2012, the FERC issued an order concluding that Ameren Illinois improperly included acquisition premiums, including goodwill, in determining the common equity used in its electric transmission formula rate and thereby inappropriately recovered a higher amount from its electric transmission customers. The order required Ameren Illinois to make refunds to customers for such improperly included amounts. In July 2015, the FERC approved a settlement agreement between Ameren Illinois and the affected customers. The settlement agreement requires Ameren Illinois to make refunds and payments of $8 million to electric transmission customers, of which $6 million was outstanding as of June 30, 2015. Ameren Illinois refunded $2 million in the second quarter of 2015 as part of a separate proceeding. The settlement agreement also requires Ameren Illinois to take other actions, such as reducing common equity for electric transmission ratemaking purposes on a prospective basis. FERC Complaint Cases In November 2013, a customer group filed a complaint case with the FERC seeking a reduction in the allowed base return on common equity for the FERC-regulated MISO transmission rate base under the MISO tariff to 9.15%. Currently, the FERC-allowed base return on common equity for MISO transmission owners is 12.38%. The FERC scheduled the case for hearing proceedings, requiring a proposed order from its administrative law judge to be issued no later than November 30, 2015, which will subsequently require FERC approval. The FERC has previously utilized a calculation to establish the allowed base return on common equity, which requires multiple inputs based on observable market data specific to the utility industry and broader macroeconomic data spanning unique time periods for each return on equity complaint case. We expect observable market data for the six months ended February 11, 2015 will be used in the November 2013 complaint case. As the maximum FERC-allowed refund period for the November 2013 complaint case ended in February 2015, another customer complaint case was filed in February 2015. The February 2015 complaint case seeks a reduction in the allowed base return on common equity for the FERC-regulated MISO transmission rate base under the MISO tariff to 8.67%. The FERC scheduled the February 2015 complaint case for hearing proceedings, requiring a proposed order from its administrative law judge to be issued no later than June 30, 2016, which will subsequently require FERC approval. We expect observable market data for the six months ended December 31, 2015 will be used in the February 2015 complaint case. A 50 basis point reduction in the FERC-allowed return on common equity would reduce Ameren's and Ameren Illinois' annual earnings by an estimated $4 million and $2 million, respectively, based on 2015 projected rate base. Ameren and Ameren Illinois recorded current liabilities on their respective balance sheets as of June 30, 2015 representing their estimate of the potential refunds from the refund effective date of November 12, 2013. Ameren’s and Ameren Illinois’ recorded liabilities reflect the inputs used in the FERC’s calculation to establish the allowed base return on common equity, based on observable market data for the six months ended February 11, 2015, with respect to the November 2013 complaint case refund period, and based on current market data through June 30, 2015, with respect to the February 2015 complaint case refund period. Ameren’s and Ameren Illinois’ liabilities also reflect the 50 basis point adder discussed below, which became effective in early January 2015. Ameren Missouri did not record a liability as of June 30, 2015, and does not expect that a reduction in the FERC-allowed base return on common equity for MISO transmission owners would be material to its results of operations, financial position, or liquidity. On January 6, 2015, a FERC-approved incentive adder of up to 50 basis points on the allowed base return on common equity for our participation in an RTO became effective. Collection of the incentive adder is deferred until the issuance of the final order addressing the initial MISO complaint case. Combined Construction and Operating License In 2008, Ameren Missouri filed an application with the NRC for a COL for a second nuclear unit at Ameren Missouri's existing Callaway County, Missouri, energy center site. In 2009, Ameren Missouri suspended its efforts to build a second nuclear unit at its existing Callaway site, and the NRC suspended review of the COL application. Prior to suspending its efforts, Ameren Missouri had capitalized $69 million related to the project. Due primarily to recent changes in vendor support for licensing efforts at the NRC, our assessment of long-term capacity needs, declining costs of alternative generation technologies, and the regulatory framework in Missouri, Ameren Missouri discontinued its efforts to license and build a second nuclear unit at its existing Callaway site. As a result of this decision, in the second quarter of 2015, Ameren and Ameren Missouri recognized a $69 million noncash pretax provision for all of the previously capitalized costs of the COL. Ameren Missouri intends to withdraw its COL application filed with the NRC in August 2015.

RATE AND REGULATORY MATTERS

Below is a summary of updates to significant regulatory proceedings and related lawsuits. See also Note 2 - Rate and Regulatory Matters under Part II, Item 8, of the Form 10-K. We are unable to predict the ultimate outcome of these matters, the timing of the final decisions of the various agencies and courts, or the impact on our results of operations, financial position, or liquidity.

Missouri

2015 Electric Rate Order

In April 2015, the MoPSC issued an order approving an increase in Ameren Missouri’s annual revenues for electric service of $122 million, including $109 million related to the increase in net energy costs above those included in base rates previously authorized by the MoPSC. The remaining increase of $13 million approved by the order was for non-energy costs. The revenue increase was based on a 9.53% return on common equity, a capital structure composed of 51.8% common equity, and a rate base of $7.0 billion to reflect investments through December 31, 2014. Rate changes consistent with the order became effective on May 30, 2015.

The order approved Ameren Missouri’s request for continued use of the FAC; however, it changed the FAC to exclude all transmission revenues and substantially all transmission charges. In addition, the order did not approve the continued use of the regulatory tracking mechanisms for storm costs and vegetation management and infrastructure inspection costs. These changes to Ameren Missouri’s recovery mechanisms are expected to contribute to regulatory lag. The order did approve the continued use of the regulatory tracking mechanisms for pension and other postretirement benefits, renewable energy standard costs, solar rebates, and uncertain tax positions that the MoPSC authorized in earlier electric rate orders.

In addition, the order approved a reduction to Noranda’s electric rates with an offsetting increase in electric rates for Ameren Missouri’s other customers. The rate shift is revenue neutral to Ameren Missouri.

In June 2015, Ameren Missouri filed a notice of appeal with the Missouri Court of Appeals, Western District, reserving the right to appeal the exclusion of all transmission revenues and substantially all transmission charges from the FAC, the reduction to Noranda’s electric rates, and the level of Noranda’s sales volume included in the MoPSC’s order.

MEEIA Filing

The MEEIA established a regulatory framework that, among other things, requires the MoPSC to ensure that a utility’s financial incentives are aligned to help customers use energy more efficiently, to provide timely cost recovery, and to provide earnings opportunities associated with cost effective energy efficiency programs. Missouri does not have a law mandating energy efficiency standards.

In August 2012, the MoPSC approved Ameren Missouri’s customer energy efficiency programs, net shared benefits, and performance incentive for 2013 through 2015. The 2013 through 2015 plan anticipated Ameren Missouri would invest up to $147 million in customer energy efficiency programs, realize $100 million of net shared benefits, and be eligible for a performance incentive that would allow Ameren Missouri the potential to earn additional revenues by achieving certain customer energy efficiency goals, including $19 million if 100% of the goals are achieved during the three-year period. From January 2013 through June 2015, Ameren Missouri invested $95 million in customer energy efficiency programs and realized $115 million of net shared benefits. Ameren Missouri has not recorded revenues associated with the performance incentive, but does expect to exceed 100% of the customer energy efficiency goals by the end of 2015, subject to MoPSC review, and therefore expects to recognize revenues in excess of $19 million within the next two years.

In December 2014, Ameren Missouri filed a three-year energy efficiency plan with the MoPSC under the MEEIA for 2016 to 2018 that included a portfolio of customer energy efficiency programs along with a rider to collect the program costs, net shared benefits, and a performance incentive from customers. Ameren Missouri amended this proposed plan in June 2015 when it filed a non-unanimous stipulation and agreement with certain intervenor parties. If this plan is approved by the MoPSC, beginning in January 2016, Ameren Missouri intends to invest up to $197 million over three years in the proposed customer energy efficiency programs. Ameren Missouri requested continued use of a MEEIA rider, which allows Ameren Missouri to collect from, or refund to, customers any difference in the actual amounts incurred and the amounts collected from customers for the MEEIA program costs and net shared benefits. Ameren Missouri anticipates net shared benefits would be approximately $65 million during this three-year plan. In addition, similar to its existing MEEIA energy efficiency plan that ends in December 2015, Ameren Missouri requested a performance incentive that would allow it to potentially earn additional revenues by achieving certain customer energy efficiency goals, including $30 million if 100% of the goals are achieved during the three-year period. Ameren Missouri would need to achieve at least 70% of its customer energy efficiency goals before it earns a performance incentive.

In July 2015, the MoPSC staff and certain intervenor parties filed a non-unanimous stipulation and agreement that is unacceptable to Ameren Missouri. Even if approved by the MoPSC, Ameren Missouri is not required to implement an energy efficiency plan. There is no date by which the MoPSC must act with respect to the proposed customer energy efficiency plan. Ameren Missouri cannot predict the level of investment, net shared benefits, or performance incentive that the MoPSC may approve, if any, or whether it will ultimately implement a customer energy efficiency plan for the three-year period beginning in January 2016.

Noranda Contract Notification

Ameren Missouri supplies electricity to Noranda’s aluminum smelter in southeast Missouri under a long-term power supply agreement. In May 2015, Ameren Missouri notified Noranda of its intent to terminate the agreement effective June 1, 2020. In order to remove Noranda from its service territory, Ameren Missouri would also be required to obtain approval from the MoPSC. Sales to Noranda represented 5% of Ameren Missouri’s total electric revenue in 2014.

ATXI Transmission Projects

In May 2015, the MoPSC granted ATXI a certificate of convenience and necessity for the seven mile portion of the Illinois Rivers project located in Missouri.

In June 2015, ATXI made a filing with the MoPSC requesting a certificate of convenience and necessity for the Mark Twain project. The Mark Twain project is a MISO-approved 100-mile transmission line located in northeast Missouri. A decision is expected from the MoPSC in 2016.

Illinois

IEIMA

Under the provisions of the IEIMA’s formula rate framework, which currently extends through 2019, Ameren Illinois’ electric delivery service rates are subject to an annual revenue requirement reconciliation to its actual costs.Throughout each year, Ameren Illinois records a regulatory asset or a regulatory liability and a corresponding increase or decrease to operating revenues for any differences between the revenue requirement reflected in customer rates for that year and its estimate of the probable increase or decrease in the revenue requirement expected to ultimately be approved by the ICC based on that year's actual costs incurred. As of June 30, 2015, Ameren Illinois had recorded regulatory assets of $24 million, $102 million, and $36 million, to reflect its expected 2015, 2014, and 2013 revenue requirement reconciliation adjustments, with interest, respectively. Ameren Illinois is collecting the 2013 revenue requirement reconciliation adjustment from customers during 2015.

In April 2015, Ameren Illinois filed with the ICC its annual electric delivery service formula rate update to establish the revenue requirement used for 2016 customer rates. Pending ICC approval, and if approved as filed, Ameren Illinois’ update filing would result in a $110 million increase in Ameren Illinois’ electric delivery service revenue requirement, beginning in January 2016. This update reflects an increase to the annual formula rate based on 2014 actual costs and expected net plant additions for 2015, an increase to include the 2014 revenue requirement reconciliation adjustment, and a decrease for the conclusion of the 2013 revenue requirement reconciliation adjustment, which will be fully collected from customers in 2015. In July 2015, the ICC staff submitted its calculation of the revenue requirement included in Ameren Illinois’ update filing. The ICC staff recommended adjustments that would result in a $107 million increase in Ameren Illinois’ electric delivery service revenue requirement. An ICC decision on this April 2015 filing is expected by December 2015.

2015 Natural Gas Delivery Service Rate Case

In January 2015, Ameren Illinois filed a request with the ICC seeking approval to increase its annual revenues for natural gas delivery service. In an attempt to reduce regulatory lag, Ameren Illinois used a 2016 future test year in this proceeding. Additionally, the request included a proposal to implement a volume balancing adjustment for residential and small nonresidential customers. The volume balancing adjustment would ensure that changes in natural gas sales volumes do not result in an over or under collection of natural gas revenues for these rate classes. This case includes a capital structure composed of 50% common equity and a rate base of $1.2 billion. In July 2015, Ameren Illinois, the ICC staff, and certain other intervenors filed a stipulation and agreement with the ICC that would result in rates that are based on a return on common equity of 9.6%. The agreement does not address all the positions with all of the parties in the case. Based on the terms in the agreement and the unresolved positions in the case, Ameren Illinois' request seeks an annual revenue increase of $45 million, which Ameren Illinois estimates is materially identical to the ICC staff’s recommendation. The ICC staff and other intervenors did not oppose the volume balancing adjustment.

A decision by the ICC in this proceeding is required by December 2015, with new rates expected to be effective in January 2016. Ameren Illinois cannot predict the level of any delivery service rate changes the ICC may approve, whether the ICC will approve the volume balancing adjustment, or if the ICC will approve the agreement between Ameren Illinois, the ICC staff, and certain other intervenors. In addition, Ameren Illinois cannot predict whether any rate changes that may eventually be approved will be sufficient to enable Ameren Illinois to recover its costs and to earn a reasonable return on investments when the rate changes go into effect.

2013 Natural Gas Delivery Service Rate Order

In December 2013, the ICC issued a rate order that approved an increase in Ameren Illinois’ revenues for natural gas delivery service based on a 9.1% return on common equity. In March 2014, Ameren Illinois filed with the Appellate Court of the Fourth District of Illinois an appeal of the allowed return on common equity included in the ICC's order. Ameren Illinois sought a 10.4% return on common equity in this rate case. In June 2015, the Appellate Court of the Fourth District upheld the ICC’s rate order. Ameren Illinois does not intend to pursue any further appeals.

2015 ICC Purchased Power Reconciliation

In January 2015, the ICC issued an order that approved Ameren Illinois' reconciliation of revenues collected under its purchased power rider mechanism and Ameren Illinois' related cumulative power usage cost. In the first quarter of 2015, based on the January 2015 order, both Ameren and Ameren Illinois recorded a $15 million increase to electric revenues for the recovery of this cumulative power usage cost from electric customers.

ATXI Transmission Project

In July 2015, Illinois administrative law judges issued a proposed order that recommended a certificate of public convenience and necessity and project approval for the Spoon River project. The Spoon River project is a MISO-approved 35-mile transmission line to be constructed in northwest Illinois. A final order from the ICC is expected in 2015. A certificate of public convenience and necessity is required before ATXI can proceed with right-of-way acquisition.

Federal

Ameren Illinois Electric Transmission Rate Refund

In July 2012, the FERC issued an order concluding that Ameren Illinois improperly included acquisition premiums, including goodwill, in determining the common equity used in its electric transmission formula rate and thereby inappropriately recovered a higher amount from its electric transmission customers. The order required Ameren Illinois to make refunds to customers for such improperly included amounts.

In July 2015, the FERC approved a settlement agreement between Ameren Illinois and the affected customers. The settlement agreement requires Ameren Illinois to make refunds and payments of $8 million to electric transmission customers, of which $6 million was outstanding as of June 30, 2015. Ameren Illinois refunded $2 million in the second quarter of 2015 as part of a separate proceeding. The settlement agreement also requires Ameren Illinois to take other actions, such as reducing common equity for electric transmission ratemaking purposes on a prospective basis.

FERC Complaint Cases

In November 2013, a customer group filed a complaint case with the FERC seeking a reduction in the allowed base return on common equity for the FERC-regulated MISO transmission rate base under the MISO tariff to 9.15%. Currently, the FERC-allowed base return on common equity for MISO transmission owners is 12.38%. The FERC scheduled the case for hearing proceedings, requiring a proposed order from its administrative law judge to be issued no later than November 30, 2015, which will subsequently require FERC approval. The FERC has previously utilized a calculation to establish the allowed base return on common equity, which requires multiple inputs based on observable market data specific to the utility industry and broader macroeconomic data spanning unique time periods for each return on equity complaint case. We expect observable market data for the six months ended February 11, 2015 will be used in the November 2013 complaint case. As the maximum FERC-allowed refund period for the November 2013 complaint case ended in February 2015, another customer complaint case was filed in February 2015. The February 2015 complaint case seeks a reduction in the allowed base return on common equity for the FERC-regulated MISO transmission rate base under the MISO tariff to 8.67%. The FERC scheduled the February 2015 complaint case for hearing proceedings, requiring a proposed order from its administrative law judge to be issued no later than June 30, 2016, which will subsequently require FERC approval. We expect observable market data for the six months ended December 31, 2015 will be used in the February 2015 complaint case.

A 50 basis point reduction in the FERC-allowed return on common equity would reduce Ameren's and Ameren Illinois' annual earnings by an estimated $4 million and $2 million, respectively, based on 2015 projected rate base. Ameren and Ameren Illinois recorded current liabilities on their respective balance sheets as of June 30, 2015 representing their estimate of the potential refunds from the refund effective date of November 12, 2013. Ameren’s and Ameren Illinois’ recorded liabilities reflect the inputs used in the FERC’s calculation to establish the allowed base return on common equity, based on observable market data for the six months ended February 11, 2015, with respect to the November 2013 complaint case refund period, and based on current market data through June 30, 2015, with respect to the February 2015 complaint case refund period. Ameren’s and Ameren Illinois’ liabilities also reflect the 50 basis point adder discussed below, which became effective in early January 2015. Ameren Missouri did not record a liability as of June 30, 2015, and does not expect that a reduction in the FERC-allowed base return on common equity for MISO transmission owners would be material to its results of operations, financial position, or liquidity.

On January 6, 2015, a FERC-approved incentive adder of up to 50 basis points on the allowed base return on common equity for our participation in an RTO became effective. Collection of the incentive adder is deferred until the issuance of the final order addressing the initial MISO complaint case.

Combined Construction and Operating License

In 2008, Ameren Missouri filed an application with the NRC for a COL for a second nuclear unit at Ameren Missouri's existing Callaway County, Missouri, energy center site. In 2009, Ameren Missouri suspended its efforts to build a second nuclear unit at its existing Callaway site, and the NRC suspended review of the COL application. Prior to suspending its efforts, Ameren Missouri had capitalized $69 million related to the project. Due primarily to recent changes in vendor support for licensing efforts at the NRC, our assessment of long-term capacity needs, declining costs of alternative generation technologies, and the regulatory framework in Missouri, Ameren Missouri discontinued its efforts to license and build a second nuclear unit at its existing Callaway site. As a result of this decision, in the second quarter of 2015, Ameren and Ameren Missouri recognized a $69 million noncash pretax provision for all of the previously capitalized costs of the COL. Ameren Missouri intends to withdraw its COL application filed with the NRC in August 2015.