Rate And Regulatory Matters	3 Months Ended
Rate And Regulatory Matters	Mar. 31, 2012
Rate And Regulatory Matters	NOTE 2 - RATE AND REGULATORY MATTERS Below is a summary of 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 2009 Electric Rate Order In November 2011, the Missouri Court of Appeals issued a ruling that upheld the MoPSC's January 2009 electric rate order. In March 2012, the Circuit Court of Stoddard County, Missouri released to Ameren Missouri all of the funds held in its registry relating to the stay, which totaled $21 million, reducing previously recorded trade accounts receivable. 2010 Electric Rate Order The MIEC and MoOPC appealed certain aspects of the MoPSC's electric rate order issued in May 2010 to the Cole County Circuit Court. In addition to the MIEC appeal, four industrial customers, who are members of MIEC, also were granted a stay by the Cole County Circuit Court of the 2010 electric rate increase and the 2009 electric rate increase that was also under appeal as it applied specifically to their electric service accounts until the court rendered its decision on the appeals. As of March 31, 2012, the amount held by the Cole County Circuit Court registry relating to the stay was $16 million. This amount was reflected in "Accounts receivable-trade" on Ameren's and Ameren Missouri's balance sheets at March 31, 2012. With the resolution of the 2009 electric rate order appeal, the amount held by the Cole County Circuit Court exceeded the amount relating to the appealed issues of the MoPSC's 2010 electric rate order. Therefore, in May 2012, Ameren Missouri received $14 million from the Cole Country Circuit Court's registry. The remaining $2 million in the Cole County Circuit Court's registry will stay until this proceeding is ultimately resolved. If the MoPSC's 2010 electric rate order is ultimately upheld, Ameren Missouri will receive all of the remaining funds held in the Cole County Circuit Court's registry, plus accrued interest. If Ameren Missouri were to conclude that some portion of the rate increase resulting from the 2010 electric rate order was probable of refund to Ameren Missouri's customers, a charge to earnings would be recorded for the estimated amount of refund in the period in which that determination was made. At this time, Ameren Missouri does not believe any aspect of the 2010 MoPSC's electric rate order is probable of refund to Ameren Missouri's customers. Therefore, no reserve has been established. 2011 Electric Rate Order In July 2011, the MoPSC issued an order approving an increase for Ameren Missouri in annual revenues for electric service of $173 million. The MoPSC order disallowed the recovery of all costs of enhancements, or costs that would have been incurred absent the breach, related to the rebuilding of the Taum Sauk energy center in excess of amounts recovered from property insurance. In August 2011, Ameren Missouri appealed the disallowance of Taum Sauk enhancements to the Missouri Court of Appeals, Western District. A decision is expected by the Missouri Court of Appeals, Western District, in 2012. Ameren Missouri cannot predict the ultimate outcome of its appeal. Pending Electric Rate Case On February 3, 2012, Ameren Missouri filed a request with the MoPSC to increase its annual revenue for electric service by $376 million. The annual increase request included $81 million for recovery of the costs associated with energy efficiency programs under the MEEIA, which are discussed below. As part of its filing, Ameren Missouri requested that the MoPSC approve the implementation of a storm cost tracking mechanism, as well as plant-in-service accounting treatment. A decision by the MoPSC in this proceeding is expected in December 2012. Ameren Missouri cannot predict the level of any electric service rate change the MoPSC may approve, when any rate change may go into effect, or whether any rate increase that may eventually be approved will be sufficient for Ameren Missouri to recover its costs and earn a reasonable return on its investments when the increase goes into effect. MEEIA Filing In January 2012, Ameren Missouri made its initial filing with the MoPSC under the MEEIA. This filing proposed a three-year plan that includes a portfolio of energy efficiency programs along with a cost-recovery mechanism. If the proposal is approved, beginning in January 2013, Ameren Missouri plans to invest $145 million over three years for the proposed energy efficiency programs. Ameren Missouri is also seeking recovery of fixed costs that would not otherwise be recovered due to the effects on customer usage from energy efficiency programs in the same year the usage reduction occurs. In April 2012, the MoPSC staff issued a recommendation in response to Ameren Missouri's MEEIA filing. The MoPSC staff agreed with Ameren Missouri's request for contemporaneous recovery of program costs but rejected Ameren Missouri's request to recover fixed costs in the same year the energy efficiency related usage reductions occur. Instead, the MoPSC staff recommended that the recovery of the otherwise unrecoverable fixed costs occur beginning on January 1 of the third year after the usage reduction occurs and has been verified by an independent evaluator. A decision by the MoPSC in this proceeding is anticipated in the third quarter of 2012. The MoPSC's order in this proceeding will not affect Ameren Missouri rates until these rates are included in an electric service rate case. Ameren Missouri anticipates that the impacts of the MoPSC's decision in this MEEIA filing will be included in rates set under its pending electric service rate case that was filed on February 3, 2012, with a true-up date of July 31, 2012. Ameren Missouri's pending electric rate case includes an annual revenue increase of $81 million related to its planned portfolio of energy efficiency programs included in its MEEIA filing. FAC Prudence Review Missouri law requires the MoPSC to complete prudence reviews of Ameren Missouri's FAC at least every 18 months. In April 2011, the MoPSC issued an order with respect to its review of Ameren Missouri's FAC for the period from March 1, 2009, to September 30, 2009. In this order, the MoPSC ruled that Ameren Missouri should have included in the FAC calculation all revenues and costs associated with certain long-term partial requirements sales that were made by Ameren Missouri because of the loss of Noranda's load caused by a severe ice storm in January 2009. As a result of the order, Ameren Missouri recorded a pretax charge to earnings of $18 million, including $1 million for interest, in 2011 for its obligation to refund to Ameren Missouri's electric customers the earnings associated with these sales previously recognized by Ameren Missouri during the period from March 1, 2009, to September 30, 2009. Ameren Missouri expects to have refunded the $18 million by the end of May 2012. Ameren Missouri disagrees with the MoPSC order's classification of these sales and believes that the terms of its FAC tariff did not provide for the inclusion of these sales in the FAC calculation. In June 2011, Ameren Missouri filed an appeal with the Cole County Circuit Court. A decision is expected from the Cole County Circuit Court in 2012. Separately, in July 2011, Ameren Missouri filed a request with the MoPSC for an accounting authority order that would allow Ameren Missouri to defer, as a regulatory asset, fixed costs totaling $36 million that were not recovered from Noranda as a result of the loss of load caused by the severe 2009 ice storm for potential recovery in a future electric rate case. We cannot predict the ultimate outcome of these regulatory or judicial proceedings. In February 2012, the MoPSC staff issued its FAC review report for the period from October 1, 2009, to May 31, 2011. In its report, the MoPSC staff's position directed Ameren Missouri to refund to customers the pretax earnings associated with the same long-term partial requirements sales contracts subsequent to September 30, 2009. The MoPSC staff calculated these pretax earnings to be $26 million. We cannot predict whether the MoPSC will approve the MoPSC staff's position. If Ameren Missouri were to determine that these sales were probable of refund to Ameren Missouri's electric customers, a charge to earnings would be recorded for the refund in the period in which that determination was made. Ameren Missouri does not currently believe these amounts are probable of refund to customers. Illinois IEIMA On January 3, 2012, Ameren Illinois elected to participate in the performance-based formula ratemaking process established pursuant to the IEIMA by filing initial performance-based formula rates with the ICC. The initial filing, based on 2010 recoverable costs and expected net plant additions for 2011 and 2012, will result in new electric delivery service rates in October 2012. In its initial filing, if approved by the ICC, Ameren Illinois' calculation would result in a decrease of $19 million in its annual electric delivery service revenues. In April 2012, the ICC staff submitted its calculation of Ameren Illinois' initial filing's revenue requirement and recommended a decrease of $25 million in Ameren Illinois' annual electric delivery service revenues. The ICC deadline to approve the initial formula rates is September 28, 2012, with the rates becoming effective no later than 30 days after the ICC's decision. The rates resulting from the initial filing will be effective from October through the end of 2012. On April 20, 2012, Ameren Illinois filed a request with the ICC to update its electric delivery service revenue requirement based on 2011 recoverable costs and expected net plant additions for 2012. The update filing will result in new electric delivery service rates on January 1, 2013. Pending ICC approval, the update filing will result in an annual decrease of $15 million in Ameren Illinois' revenues for electric delivery service below the amount Ameren Illinois requested in its January 3, 2012 initial filing. The reduction primarily reflects rate base reductions due to increases in accumulated deferred income taxes, as well as a lower return on equity due to decreases in the average 30-year United States treasury bond rates. The IEIMA provides for an annual reconciliation of the revenue requirement necessary to reflect the actual costs incurred in a given year with the revenue requirement that was in effect for that year. Consequently, Ameren Illinois' 2012 electric delivery service revenues will be based on its 2012 actual recoverable costs, rate base, and return on common equity as calculated under the IEIMA's performance-based formula ratemaking framework. As a result, throughout the year, Ameren Illinois will estimate the expected future recovery or return of revenue as a regulatory asset or liability. As of March 31, 2012, Ameren Illinois recorded a regulatory asset of $12 million with a corresponding increase in electric revenues for the estimated first quarter portion of the 2012 revenue requirement reconciliation adjustment. By the end of 2012, this regulatory asset will represent Ameren Illinois' estimate of the probable increase in electric delivery service rates, compared to current and proposed rates, expected to be approved by the ICC to provide Ameren Illinois recovery of all prudently and reasonably incurred costs in 2012 and an earned rate of return on common equity for 2012. The regulatory asset relating to the 2012 revenue requirement reconciliation will be recovered from customers during 2014. Federal Electric Transmission Investment In February 2012, FERC approved ATXI's request for a forward-looking rate calculation with an annual reconciliation adjustment as well as ATXI's request for the implementation of the incentives FERC approved in its May 2011 order for the Illinois Rivers project and the Big Muddy project. 2011 Wholesale Distribution Rate Case In January 2011, Ameren Illinois filed a request with FERC to increase its annual revenues for electric delivery service for its wholesale customers by $11 million. These wholesale distribution revenues are treated as a deduction from Ameren Illinois' revenue requirement in retail rate filings with the ICC. In March 2011, FERC issued an order authorizing the proposed rates to take effect, subject to refund when the final rates are determined. Ameren Illinois reached an agreement with two of its nine wholesale customers in 2011. The impasse with the remaining seven wholesale customers has resulted in FERC litigation. An initial decision by the FERC administrative law judge is expected in 2012, and a final FERC decision may be received after 2012. We cannot predict the ultimate outcome of this proceeding or its impact on Ameren's or Ameren Illinois' results of operations, financial position, or liquidity. Regional Transmission Organization Ameren Missouri is a transmission owning member of MISO. In April 2012, the MoPSC authorized Ameren Missouri's continued participation in MISO through May 31, 2016, subject to certain conditions. By November 2015, Ameren Missouri will have to file an updated cost benefit study with the MoPSC evaluating the costs and benefits of Ameren Missouri's continued participation in MISO. Combined Construction and Operating License In 2008, Ameren Missouri filed an application with the NRC for a COL for a new 1,600-megawatt nuclear unit at Ameren Missouri's existing Callaway County, Missouri, nuclear energy center site. In 2009, Ameren Missouri suspended its efforts to build a new nuclear unit at its existing Missouri nuclear energy center site, and the NRC suspended review of the COL application. In March 2012, the DOE announced the availability of $452 million of investment funds for the design, engineering, manufacturing, and sale of American-made small modular reactors. In April 2012, Ameren Missouri entered into an agreement with Westinghouse to exclusively support Westinghouse's application for the DOE's small modular reactor investment funds. The DOE investment funding is intended to support engineering and design certifications and a COL for up to two small modular reactor designs over five years. Westinghouse expects to submit its application to the DOE in May 2012. The DOE is expected to issue a decision on awarding the investment funds in the summer of 2012. If Westinghouse is awarded DOE's small modular reactor investment funds, Ameren Missouri will seek a COL from the NRC for a Westinghouse small modular reactor at its Callaway County, Missouri nuclear energy center site. A COL is issued by the NRC to permit construction and operation of a nuclear power plant at a specific site in accordance with established laws and regulations. Obtaining a COL from the NRC does not obligate Ameren Missouri to build a small modular reactor at the Callaway site; however, it does preserve the option to move forward in a timely fashion should conditions be right to build a small modular reactor in the future. A COL is valid for at least 40 years. Ameren Missouri estimates the total cost to obtain the small modular reactor COL will be in the range of $80 million to $100 million. Ameren Missouri expects its incremental investment to obtain the small modular reactor COL will be minimal due to several factors, including the company's capitalized investments of $69 million as of March 31, 2012, in new nuclear energy center development, the DOE investment funds that would help support the COL application, and its agreement with Westinghouse. If the DOE does not approve Westinghouse's application for the small modular reactor investment funds, Ameren Missouri is not obligated to pursue a COL for the Westinghouse small modular reactor design and may terminate its agreement with Westinghouse. All of Ameren Missouri's costs incurred to construct a new nuclear unit will remain capitalized while management pursues options to maximize the value of its investment in this project. If efforts are permanently abandoned or management concludes it is probable the costs incurred will be disallowed in rates, a charge to earnings would be recognized in the period in which that determination was made.
Ameren Illinois Company [Member]
Rate And Regulatory Matters	NOTE 2 - RATE AND REGULATORY MATTERS Below is a summary of 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 2009 Electric Rate Order In November 2011, the Missouri Court of Appeals issued a ruling that upheld the MoPSC's January 2009 electric rate order. In March 2012, the Circuit Court of Stoddard County, Missouri released to Ameren Missouri all of the funds held in its registry relating to the stay, which totaled $21 million, reducing previously recorded trade accounts receivable. 2010 Electric Rate Order The MIEC and MoOPC appealed certain aspects of the MoPSC's electric rate order issued in May 2010 to the Cole County Circuit Court. In addition to the MIEC appeal, four industrial customers, who are members of MIEC, also were granted a stay by the Cole County Circuit Court of the 2010 electric rate increase and the 2009 electric rate increase that was also under appeal as it applied specifically to their electric service accounts until the court rendered its decision on the appeals. As of March 31, 2012, the amount held by the Cole County Circuit Court registry relating to the stay was $16 million. This amount was reflected in "Accounts receivable-trade" on Ameren's and Ameren Missouri's balance sheets at March 31, 2012. With the resolution of the 2009 electric rate order appeal, the amount held by the Cole County Circuit Court exceeded the amount relating to the appealed issues of the MoPSC's 2010 electric rate order. Therefore, in May 2012, Ameren Missouri received $14 million from the Cole Country Circuit Court's registry. The remaining $2 million in the Cole County Circuit Court's registry will stay until this proceeding is ultimately resolved. If the MoPSC's 2010 electric rate order is ultimately upheld, Ameren Missouri will receive all of the remaining funds held in the Cole County Circuit Court's registry, plus accrued interest. If Ameren Missouri were to conclude that some portion of the rate increase resulting from the 2010 electric rate order was probable of refund to Ameren Missouri's customers, a charge to earnings would be recorded for the estimated amount of refund in the period in which that determination was made. At this time, Ameren Missouri does not believe any aspect of the 2010 MoPSC's electric rate order is probable of refund to Ameren Missouri's customers. Therefore, no reserve has been established. 2011 Electric Rate Order In July 2011, the MoPSC issued an order approving an increase for Ameren Missouri in annual revenues for electric service of $173 million. The MoPSC order disallowed the recovery of all costs of enhancements, or costs that would have been incurred absent the breach, related to the rebuilding of the Taum Sauk energy center in excess of amounts recovered from property insurance. In August 2011, Ameren Missouri appealed the disallowance of Taum Sauk enhancements to the Missouri Court of Appeals, Western District. A decision is expected by the Missouri Court of Appeals, Western District, in 2012. Ameren Missouri cannot predict the ultimate outcome of its appeal. Pending Electric Rate Case On February 3, 2012, Ameren Missouri filed a request with the MoPSC to increase its annual revenue for electric service by $376 million. The annual increase request included $81 million for recovery of the costs associated with energy efficiency programs under the MEEIA, which are discussed below. As part of its filing, Ameren Missouri requested that the MoPSC approve the implementation of a storm cost tracking mechanism, as well as plant-in-service accounting treatment. A decision by the MoPSC in this proceeding is expected in December 2012. Ameren Missouri cannot predict the level of any electric service rate change the MoPSC may approve, when any rate change may go into effect, or whether any rate increase that may eventually be approved will be sufficient for Ameren Missouri to recover its costs and earn a reasonable return on its investments when the increase goes into effect. MEEIA Filing In January 2012, Ameren Missouri made its initial filing with the MoPSC under the MEEIA. This filing proposed a three-year plan that includes a portfolio of energy efficiency programs along with a cost-recovery mechanism. If the proposal is approved, beginning in January 2013, Ameren Missouri plans to invest $145 million over three years for the proposed energy efficiency programs. Ameren Missouri is also seeking recovery of fixed costs that would not otherwise be recovered due to the effects on customer usage from energy efficiency programs in the same year the usage reduction occurs. In April 2012, the MoPSC staff issued a recommendation in response to Ameren Missouri's MEEIA filing. The MoPSC staff agreed with Ameren Missouri's request for contemporaneous recovery of program costs but rejected Ameren Missouri's request to recover fixed costs in the same year the energy efficiency related usage reductions occur. Instead, the MoPSC staff recommended that the recovery of the otherwise unrecoverable fixed costs occur beginning on January 1 of the third year after the usage reduction occurs and has been verified by an independent evaluator. A decision by the MoPSC in this proceeding is anticipated in the third quarter of 2012. The MoPSC's order in this proceeding will not affect Ameren Missouri rates until these rates are included in an electric service rate case. Ameren Missouri anticipates that the impacts of the MoPSC's decision in this MEEIA filing will be included in rates set under its pending electric service rate case that was filed on February 3, 2012, with a true-up date of July 31, 2012. Ameren Missouri's pending electric rate case includes an annual revenue increase of $81 million related to its planned portfolio of energy efficiency programs included in its MEEIA filing. FAC Prudence Review Missouri law requires the MoPSC to complete prudence reviews of Ameren Missouri's FAC at least every 18 months. In April 2011, the MoPSC issued an order with respect to its review of Ameren Missouri's FAC for the period from March 1, 2009, to September 30, 2009. In this order, the MoPSC ruled that Ameren Missouri should have included in the FAC calculation all revenues and costs associated with certain long-term partial requirements sales that were made by Ameren Missouri because of the loss of Noranda's load caused by a severe ice storm in January 2009. As a result of the order, Ameren Missouri recorded a pretax charge to earnings of $18 million, including $1 million for interest, in 2011 for its obligation to refund to Ameren Missouri's electric customers the earnings associated with these sales previously recognized by Ameren Missouri during the period from March 1, 2009, to September 30, 2009. Ameren Missouri expects to have refunded the $18 million by the end of May 2012. Ameren Missouri disagrees with the MoPSC order's classification of these sales and believes that the terms of its FAC tariff did not provide for the inclusion of these sales in the FAC calculation. In June 2011, Ameren Missouri filed an appeal with the Cole County Circuit Court. A decision is expected from the Cole County Circuit Court in 2012. Separately, in July 2011, Ameren Missouri filed a request with the MoPSC for an accounting authority order that would allow Ameren Missouri to defer, as a regulatory asset, fixed costs totaling $36 million that were not recovered from Noranda as a result of the loss of load caused by the severe 2009 ice storm for potential recovery in a future electric rate case. We cannot predict the ultimate outcome of these regulatory or judicial proceedings. In February 2012, the MoPSC staff issued its FAC review report for the period from October 1, 2009, to May 31, 2011. In its report, the MoPSC staff's position directed Ameren Missouri to refund to customers the pretax earnings associated with the same long-term partial requirements sales contracts subsequent to September 30, 2009. The MoPSC staff calculated these pretax earnings to be $26 million. We cannot predict whether the MoPSC will approve the MoPSC staff's position. If Ameren Missouri were to determine that these sales were probable of refund to Ameren Missouri's electric customers, a charge to earnings would be recorded for the refund in the period in which that determination was made. Ameren Missouri does not currently believe these amounts are probable of refund to customers. Illinois IEIMA On January 3, 2012, Ameren Illinois elected to participate in the performance-based formula ratemaking process established pursuant to the IEIMA by filing initial performance-based formula rates with the ICC. The initial filing, based on 2010 recoverable costs and expected net plant additions for 2011 and 2012, will result in new electric delivery service rates in October 2012. In its initial filing, if approved by the ICC, Ameren Illinois' calculation would result in a decrease of $19 million in its annual electric delivery service revenues. In April 2012, the ICC staff submitted its calculation of Ameren Illinois' initial filing's revenue requirement and recommended a decrease of $25 million in Ameren Illinois' annual electric delivery service revenues. The ICC deadline to approve the initial formula rates is September 28, 2012, with the rates becoming effective no later than 30 days after the ICC's decision. The rates resulting from the initial filing will be effective from October through the end of 2012. On April 20, 2012, Ameren Illinois filed a request with the ICC to update its electric delivery service revenue requirement based on 2011 recoverable costs and expected net plant additions for 2012. The update filing will result in new electric delivery service rates on January 1, 2013. Pending ICC approval, the update filing will result in an annual decrease of $15 million in Ameren Illinois' revenues for electric delivery service below the amount Ameren Illinois requested in its January 3, 2012 initial filing. The reduction primarily reflects rate base reductions due to increases in accumulated deferred income taxes, as well as a lower return on equity due to decreases in the average 30-year United States treasury bond rates. The IEIMA provides for an annual reconciliation of the revenue requirement necessary to reflect the actual costs incurred in a given year with the revenue requirement that was in effect for that year. Consequently, Ameren Illinois' 2012 electric delivery service revenues will be based on its 2012 actual recoverable costs, rate base, and return on common equity as calculated under the IEIMA's performance-based formula ratemaking framework. As a result, throughout the year, Ameren Illinois will estimate the expected future recovery or return of revenue as a regulatory asset or liability. As of March 31, 2012, Ameren Illinois recorded a regulatory asset of $12 million with a corresponding increase in electric revenues for the estimated first quarter portion of the 2012 revenue requirement reconciliation adjustment. By the end of 2012, this regulatory asset will represent Ameren Illinois' estimate of the probable increase in electric delivery service rates, compared to current and proposed rates, expected to be approved by the ICC to provide Ameren Illinois recovery of all prudently and reasonably incurred costs in 2012 and an earned rate of return on common equity for 2012. The regulatory asset relating to the 2012 revenue requirement reconciliation will be recovered from customers during 2014. Federal Electric Transmission Investment In February 2012, FERC approved ATXI's request for a forward-looking rate calculation with an annual reconciliation adjustment as well as ATXI's request for the implementation of the incentives FERC approved in its May 2011 order for the Illinois Rivers project and the Big Muddy project. 2011 Wholesale Distribution Rate Case In January 2011, Ameren Illinois filed a request with FERC to increase its annual revenues for electric delivery service for its wholesale customers by $11 million. These wholesale distribution revenues are treated as a deduction from Ameren Illinois' revenue requirement in retail rate filings with the ICC. In March 2011, FERC issued an order authorizing the proposed rates to take effect, subject to refund when the final rates are determined. Ameren Illinois reached an agreement with two of its nine wholesale customers in 2011. The impasse with the remaining seven wholesale customers has resulted in FERC litigation. An initial decision by the FERC administrative law judge is expected in 2012, and a final FERC decision may be received after 2012. We cannot predict the ultimate outcome of this proceeding or its impact on Ameren's or Ameren Illinois' results of operations, financial position, or liquidity. Regional Transmission Organization Ameren Missouri is a transmission owning member of MISO. In April 2012, the MoPSC authorized Ameren Missouri's continued participation in MISO through May 31, 2016, subject to certain conditions. By November 2015, Ameren Missouri will have to file an updated cost benefit study with the MoPSC evaluating the costs and benefits of Ameren Missouri's continued participation in MISO. Combined Construction and Operating License In 2008, Ameren Missouri filed an application with the NRC for a COL for a new 1,600-megawatt nuclear unit at Ameren Missouri's existing Callaway County, Missouri, nuclear energy center site. In 2009, Ameren Missouri suspended its efforts to build a new nuclear unit at its existing Missouri nuclear energy center site, and the NRC suspended review of the COL application. In March 2012, the DOE announced the availability of $452 million of investment funds for the design, engineering, manufacturing, and sale of American-made small modular reactors. In April 2012, Ameren Missouri entered into an agreement with Westinghouse to exclusively support Westinghouse's application for the DOE's small modular reactor investment funds. The DOE investment funding is intended to support engineering and design certifications and a COL for up to two small modular reactor designs over five years. Westinghouse expects to submit its application to the DOE in May 2012. The DOE is expected to issue a decision on awarding the investment funds in the summer of 2012. If Westinghouse is awarded DOE's small modular reactor investment funds, Ameren Missouri will seek a COL from the NRC for a Westinghouse small modular reactor at its Callaway County, Missouri nuclear energy center site. A COL is issued by the NRC to permit construction and operation of a nuclear power plant at a specific site in accordance with established laws and regulations. Obtaining a COL from the NRC does not obligate Ameren Missouri to build a small modular reactor at the Callaway site; however, it does preserve the option to move forward in a timely fashion should conditions be right to build a small modular reactor in the future. A COL is valid for at least 40 years. Ameren Missouri estimates the total cost to obtain the small modular reactor COL will be in the range of $80 million to $100 million. Ameren Missouri expects its incremental investment to obtain the small modular reactor COL will be minimal due to several factors, including the company's capitalized investments of $69 million as of March 31, 2012, in new nuclear energy center development, the DOE investment funds that would help support the COL application, and its agreement with Westinghouse. If the DOE does not approve Westinghouse's application for the small modular reactor investment funds, Ameren Missouri is not obligated to pursue a COL for the Westinghouse small modular reactor design and may terminate its agreement with Westinghouse. All of Ameren Missouri's costs incurred to construct a new nuclear unit will remain capitalized while management pursues options to maximize the value of its investment in this project. If efforts are permanently abandoned or management concludes it is probable the costs incurred will be disallowed in rates, a charge to earnings would be recognized in the period in which that determination was made.
Union Electric Company [Member]
Rate And Regulatory Matters	NOTE 2 - RATE AND REGULATORY MATTERS Below is a summary of 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 2009 Electric Rate Order In November 2011, the Missouri Court of Appeals issued a ruling that upheld the MoPSC's January 2009 electric rate order. In March 2012, the Circuit Court of Stoddard County, Missouri released to Ameren Missouri all of the funds held in its registry relating to the stay, which totaled $21 million, reducing previously recorded trade accounts receivable. 2010 Electric Rate Order The MIEC and MoOPC appealed certain aspects of the MoPSC's electric rate order issued in May 2010 to the Cole County Circuit Court. In addition to the MIEC appeal, four industrial customers, who are members of MIEC, also were granted a stay by the Cole County Circuit Court of the 2010 electric rate increase and the 2009 electric rate increase that was also under appeal as it applied specifically to their electric service accounts until the court rendered its decision on the appeals. As of March 31, 2012, the amount held by the Cole County Circuit Court registry relating to the stay was $16 million. This amount was reflected in "Accounts receivable-trade" on Ameren's and Ameren Missouri's balance sheets at March 31, 2012. With the resolution of the 2009 electric rate order appeal, the amount held by the Cole County Circuit Court exceeded the amount relating to the appealed issues of the MoPSC's 2010 electric rate order. Therefore, in May 2012, Ameren Missouri received $14 million from the Cole Country Circuit Court's registry. The remaining $2 million in the Cole County Circuit Court's registry will stay until this proceeding is ultimately resolved. If the MoPSC's 2010 electric rate order is ultimately upheld, Ameren Missouri will receive all of the remaining funds held in the Cole County Circuit Court's registry, plus accrued interest. If Ameren Missouri were to conclude that some portion of the rate increase resulting from the 2010 electric rate order was probable of refund to Ameren Missouri's customers, a charge to earnings would be recorded for the estimated amount of refund in the period in which that determination was made. At this time, Ameren Missouri does not believe any aspect of the 2010 MoPSC's electric rate order is probable of refund to Ameren Missouri's customers. Therefore, no reserve has been established. 2011 Electric Rate Order In July 2011, the MoPSC issued an order approving an increase for Ameren Missouri in annual revenues for electric service of $173 million. The MoPSC order disallowed the recovery of all costs of enhancements, or costs that would have been incurred absent the breach, related to the rebuilding of the Taum Sauk energy center in excess of amounts recovered from property insurance. In August 2011, Ameren Missouri appealed the disallowance of Taum Sauk enhancements to the Missouri Court of Appeals, Western District. A decision is expected by the Missouri Court of Appeals, Western District, in 2012. Ameren Missouri cannot predict the ultimate outcome of its appeal. Pending Electric Rate Case On February 3, 2012, Ameren Missouri filed a request with the MoPSC to increase its annual revenue for electric service by $376 million. The annual increase request included $81 million for recovery of the costs associated with energy efficiency programs under the MEEIA, which are discussed below. As part of its filing, Ameren Missouri requested that the MoPSC approve the implementation of a storm cost tracking mechanism, as well as plant-in-service accounting treatment. A decision by the MoPSC in this proceeding is expected in December 2012. Ameren Missouri cannot predict the level of any electric service rate change the MoPSC may approve, when any rate change may go into effect, or whether any rate increase that may eventually be approved will be sufficient for Ameren Missouri to recover its costs and earn a reasonable return on its investments when the increase goes into effect. MEEIA Filing In January 2012, Ameren Missouri made its initial filing with the MoPSC under the MEEIA. This filing proposed a three-year plan that includes a portfolio of energy efficiency programs along with a cost-recovery mechanism. If the proposal is approved, beginning in January 2013, Ameren Missouri plans to invest $145 million over three years for the proposed energy efficiency programs. Ameren Missouri is also seeking recovery of fixed costs that would not otherwise be recovered due to the effects on customer usage from energy efficiency programs in the same year the usage reduction occurs. In April 2012, the MoPSC staff issued a recommendation in response to Ameren Missouri's MEEIA filing. The MoPSC staff agreed with Ameren Missouri's request for contemporaneous recovery of program costs but rejected Ameren Missouri's request to recover fixed costs in the same year the energy efficiency related usage reductions occur. Instead, the MoPSC staff recommended that the recovery of the otherwise unrecoverable fixed costs occur beginning on January 1 of the third year after the usage reduction occurs and has been verified by an independent evaluator. A decision by the MoPSC in this proceeding is anticipated in the third quarter of 2012. The MoPSC's order in this proceeding will not affect Ameren Missouri rates until these rates are included in an electric service rate case. Ameren Missouri anticipates that the impacts of the MoPSC's decision in this MEEIA filing will be included in rates set under its pending electric service rate case that was filed on February 3, 2012, with a true-up date of July 31, 2012. Ameren Missouri's pending electric rate case includes an annual revenue increase of $81 million related to its planned portfolio of energy efficiency programs included in its MEEIA filing. FAC Prudence Review Missouri law requires the MoPSC to complete prudence reviews of Ameren Missouri's FAC at least every 18 months. In April 2011, the MoPSC issued an order with respect to its review of Ameren Missouri's FAC for the period from March 1, 2009, to September 30, 2009. In this order, the MoPSC ruled that Ameren Missouri should have included in the FAC calculation all revenues and costs associated with certain long-term partial requirements sales that were made by Ameren Missouri because of the loss of Noranda's load caused by a severe ice storm in January 2009. As a result of the order, Ameren Missouri recorded a pretax charge to earnings of $18 million, including $1 million for interest, in 2011 for its obligation to refund to Ameren Missouri's electric customers the earnings associated with these sales previously recognized by Ameren Missouri during the period from March 1, 2009, to September 30, 2009. Ameren Missouri expects to have refunded the $18 million by the end of May 2012. Ameren Missouri disagrees with the MoPSC order's classification of these sales and believes that the terms of its FAC tariff did not provide for the inclusion of these sales in the FAC calculation. In June 2011, Ameren Missouri filed an appeal with the Cole County Circuit Court. A decision is expected from the Cole County Circuit Court in 2012. Separately, in July 2011, Ameren Missouri filed a request with the MoPSC for an accounting authority order that would allow Ameren Missouri to defer, as a regulatory asset, fixed costs totaling $36 million that were not recovered from Noranda as a result of the loss of load caused by the severe 2009 ice storm for potential recovery in a future electric rate case. We cannot predict the ultimate outcome of these regulatory or judicial proceedings. In February 2012, the MoPSC staff issued its FAC review report for the period from October 1, 2009, to May 31, 2011. In its report, the MoPSC staff's position directed Ameren Missouri to refund to customers the pretax earnings associated with the same long-term partial requirements sales contracts subsequent to September 30, 2009. The MoPSC staff calculated these pretax earnings to be $26 million. We cannot predict whether the MoPSC will approve the MoPSC staff's position. If Ameren Missouri were to determine that these sales were probable of refund to Ameren Missouri's electric customers, a charge to earnings would be recorded for the refund in the period in which that determination was made. Ameren Missouri does not currently believe these amounts are probable of refund to customers. Illinois IEIMA On January 3, 2012, Ameren Illinois elected to participate in the performance-based formula ratemaking process established pursuant to the IEIMA by filing initial performance-based formula rates with the ICC. The initial filing, based on 2010 recoverable costs and expected net plant additions for 2011 and 2012, will result in new electric delivery service rates in October 2012. In its initial filing, if approved by the ICC, Ameren Illinois' calculation would result in a decrease of $19 million in its annual electric delivery service revenues. In April 2012, the ICC staff submitted its calculation of Ameren Illinois' initial filing's revenue requirement and recommended a decrease of $25 million in Ameren Illinois' annual electric delivery service revenues. The ICC deadline to approve the initial formula rates is September 28, 2012, with the rates becoming effective no later than 30 days after the ICC's decision. The rates resulting from the initial filing will be effective from October through the end of 2012. On April 20, 2012, Ameren Illinois filed a request with the ICC to update its electric delivery service revenue requirement based on 2011 recoverable costs and expected net plant additions for 2012. The update filing will result in new electric delivery service rates on January 1, 2013. Pending ICC approval, the update filing will result in an annual decrease of $15 million in Ameren Illinois' revenues for electric delivery service below the amount Ameren Illinois requested in its January 3, 2012 initial filing. The reduction primarily reflects rate base reductions due to increases in accumulated deferred income taxes, as well as a lower return on equity due to decreases in the average 30-year United States treasury bond rates. The IEIMA provides for an annual reconciliation of the revenue requirement necessary to reflect the actual costs incurred in a given year with the revenue requirement that was in effect for that year. Consequently, Ameren Illinois' 2012 electric delivery service revenues will be based on its 2012 actual recoverable costs, rate base, and return on common equity as calculated under the IEIMA's performance-based formula ratemaking framework. As a result, throughout the year, Ameren Illinois will estimate the expected future recovery or return of revenue as a regulatory asset or liability. As of March 31, 2012, Ameren Illinois recorded a regulatory asset of $12 million with a corresponding increase in electric revenues for the estimated first quarter portion of the 2012 revenue requirement reconciliation adjustment. By the end of 2012, this regulatory asset will represent Ameren Illinois' estimate of the probable increase in electric delivery service rates, compared to current and proposed rates, expected to be approved by the ICC to provide Ameren Illinois recovery of all prudently and reasonably incurred costs in 2012 and an earned rate of return on common equity for 2012. The regulatory asset relating to the 2012 revenue requirement reconciliation will be recovered from customers during 2014. Federal Electric Transmission Investment In February 2012, FERC approved ATXI's request for a forward-looking rate calculation with an annual reconciliation adjustment as well as ATXI's request for the implementation of the incentives FERC approved in its May 2011 order for the Illinois Rivers project and the Big Muddy project. 2011 Wholesale Distribution Rate Case In January 2011, Ameren Illinois filed a request with FERC to increase its annual revenues for electric delivery service for its wholesale customers by $11 million. These wholesale distribution revenues are treated as a deduction from Ameren Illinois' revenue requirement in retail rate filings with the ICC. In March 2011, FERC issued an order authorizing the proposed rates to take effect, subject to refund when the final rates are determined. Ameren Illinois reached an agreement with two of its nine wholesale customers in 2011. The impasse with the remaining seven wholesale customers has resulted in FERC litigation. An initial decision by the FERC administrative law judge is expected in 2012, and a final FERC decision may be received after 2012. We cannot predict the ultimate outcome of this proceeding or its impact on Ameren's or Ameren Illinois' results of operations, financial position, or liquidity. Regional Transmission Organization Ameren Missouri is a transmission owning member of MISO. In April 2012, the MoPSC authorized Ameren Missouri's continued participation in MISO through May 31, 2016, subject to certain conditions. By November 2015, Ameren Missouri will have to file an updated cost benefit study with the MoPSC evaluating the costs and benefits of Ameren Missouri's continued participation in MISO. Combined Construction and Operating License In 2008, Ameren Missouri filed an application with the NRC for a COL for a new 1,600-megawatt nuclear unit at Ameren Missouri's existing Callaway County, Missouri, nuclear energy center site. In 2009, Ameren Missouri suspended its efforts to build a new nuclear unit at its existing Missouri nuclear energy center site, and the NRC suspended review of the COL application. In March 2012, the DOE announced the availability of $452 million of investment funds for the design, engineering, manufacturing, and sale of American-made small modular reactors. In April 2012, Ameren Missouri entered into an agreement with Westinghouse to exclusively support Westinghouse's application for the DOE's small modular reactor investment funds. The DOE investment funding is intended to support engineering and design certifications and a COL for up to two small modular reactor designs over five years. Westinghouse expects to submit its application to the DOE in May 2012. The DOE is expected to issue a decision on awarding the investment funds in the summer of 2012. If Westinghouse is awarded DOE's small modular reactor investment funds, Ameren Missouri will seek a COL from the NRC for a Westinghouse small modular reactor at its Callaway County, Missouri nuclear energy center site. A COL is issued by the NRC to permit construction and operation of a nuclear power plant at a specific site in accordance with established laws and regulations. Obtaining a COL from the NRC does not obligate Ameren Missouri to build a small modular reactor at the Callaway site; however, it does preserve the option to move forward in a timely fashion should conditions be right to build a small modular reactor in the future. A COL is valid for at least 40 years. Ameren Missouri estimates the total cost to obtain the small modular reactor COL will be in the range of $80 million to $100 million. Ameren Missouri expects its incremental investment to obtain the small modular reactor COL will be minimal due to several factors, including the company's capitalized investments of $69 million as of March 31, 2012, in new nuclear energy center development, the DOE investment funds that would help support the COL application, and its agreement with Westinghouse. If the DOE does not approve Westinghouse's application for the small modular reactor investment funds, Ameren Missouri is not obligated to pursue a COL for the Westinghouse small modular reactor design and may terminate its agreement with Westinghouse. All of Ameren Missouri's costs incurred to construct a new nuclear unit will remain capitalized while management pursues options to maximize the value of its investment in this project. If efforts are permanently abandoned or management concludes it is probable the costs incurred will be disallowed in rates, a charge to earnings would be recognized in the period in which that determination was made.