Regulatory Matters	12 Months Ended
Regulatory Matters	Dec. 31, 2017
Entity Information [Line Items]
Regulatory Matters	REGULATORY MATTERS General IPL is subject to regulation by the IURC as to its services and facilities, the valuation of property, the construction, purchase, or lease of electric generating facilities, the classification of accounts, rates of depreciation, retail rates and charges, the issuance of securities (other than evidences of indebtedness payable less than twelve months after the date of issue), the acquisition and sale of some public utility properties or securities and certain other matters. In addition, IPL is subject to the jurisdiction of the FERC with respect to, among other things, short-term borrowings not regulated by the IURC, the sale of electricity at wholesale, the transmission of electric energy in interstate commerce, the classification of accounts, reliability standards, and the acquisition and sale of utility property in certain circumstances as provided by the Federal Power Act. As a regulated entity, IPL is required to use certain accounting methods prescribed by regulatory bodies which may differ from those accounting methods required to be used by unregulated entities. IPL is also affected by the regulatory jurisdiction of the EPA at the federal level, and the IDEM at the state level. Other significant regulatory agencies affecting IPL include, but are not limited to, the NERC, the U.S. Department of Labor and the IOSHA. Basic Rates and Charges Our basic rates and charges represent the largest component of our annual revenues. Our basic rates and charges are determined after giving consideration, on a pro-forma basis, to all allowable costs for ratemaking purposes including a fair return on the fair value of the utility property used and useful in providing service to customers. These basic rates and charges are set and approved by the IURC after public hearings. Such proceedings, which have occurred at irregular intervals, involve IPL, the IURC, the Indiana Office of Utility Consumer Counselor, and other interested stakeholders. Pursuant to statute, the IURC is to conduct a periodic review of the basic rates and charges of all Indiana utilities at least once every four years, but the IURC has the authority to review the rates of any Indiana utility at any time. Once set, the basic rates and charges authorized do not assure the realization of a fair return on the fair value of property. Our declining block rate structure generally provides for residential and commercial customers to be charged a lower per kWh rate at higher consumption levels. Therefore, as volumes increase, the weighted average price per kWh decreases. Numerous factors including, but not limited to, weather, inflation, customer growth and usage, the level of actual operating and maintenance expenditures, capital expenditures including those required by environmental regulations, fuel costs, and generating unit availability, can affect the return realized. In May 2014, IPL received an order from the IURC granting approval to build a 644 to 685 MW CCGT at Eagle Valley. The costs to build and operate the CCGT, other than fuel costs, will not be recoverable by IPL through rates until the conclusion of a base rate case proceeding with the IURC after construction is completed. The CCGT was originally expected to be completed in the first half of 2017 and that timing was changed in 2017 to an expected completion in the first half of 2018. IPL filed a petition with the IURC on December 21, 2017, for authority to increase its basic rates and charges to coincide with the expected completion of the CCGT in the first half of 2018. IPL’s proposed revenue increase was $124.5 million annually, or 9.1%. On February 16, 2018, IPL filed an update to such petition to reflect the federal income tax law changes passed, which reduced the revenue increase IPL is seeking to $96.7 million, or 7.1%. An order on this proceeding will likely be issued by the IURC by the first quarter of 2019. In March 2016, the IURC issued the 2016 Rate Order authorizing IPL to increase its basic rates and charges by $30.8 million annually. The order also authorized IPL to collect, over a ten year period, $117.7 million of previously deferred regulatory assets related to IPL’s participation in the regional transmission organization known as MISO. Such deferred costs are amortized to expense over ten years. Accordingly, $11.8 million of IPL’s long-term MISO regulatory asset is included within current regulatory assets on the accompanying Consolidated Balance Sheets. The rate order also authorized an increase in IPL’s depreciation rates of $24.3 million annually compared to the twelve months ended June 30, 2014, which is the period upon which the rate increase was calculated. IPL also received approval to implement three new rate riders for current recovery from customers of ongoing MISO costs and capacity costs, and for sharing with customers 50% of wholesale sales margins above and below the established benchmark of $6.3 million. Additionally, the capacity rider provides that IPL will share with customers 50% of any capacity sales. The order approved recovery of IPL’s pension expenses and a return on IPL’s discretionary pension fundings. While the IURC noted in the order that they found IPL’s Service Company cost allocations to be reasonable, IPL was directed to request the FERC to review its Service Company allocations. In September 2017, the FERC completed its review, authorizing the Service Company’s allocation of costs of non-power goods and services to IPL. In the 2016 Rate Order, the IURC also closed their investigation into IPL’s underground network. Some of the intervening parties in the IURC rate case filed petitions for reconsideration of the IURC’s March 2016 order with respect to certain issues. These petitions were subsequently denied by the IURC. In addition, certain intervening parties filed notices of appeal of the order. On April 5, 2017, the Indiana Court of Appeals affirmed the IURC’s March 2016 order. CCR On April 26, 2017, the IURC approved IPL’s CCR compliance request to install a bottom ash dewatering system at its Petersburg generating station and to recover 80% of qualifying costs through a rate adjustment mechanism with the remainder recorded as a regulatory asset for recovery in a subsequent rate case. The approved capital cost of the CCR compliance plan is approximately $47 million. IPL’s bottom ash dewatering system at its Petersburg generating station went into service in September 2017. NAAQS On April 26, 2017, the IURC approved IPL’s request for NAAQS SO2 compliance at its Petersburg generation station with 80% of qualifying costs recovered through a rate adjustment mechanism and the remainder recorded as a regulatory asset for recovery in a subsequent rate case. The approved capital cost of the NAAQS SO2 compliance plan is approximately $29 million. This project is expected to be fully in service in the first quarter of 2019. Other The DOE issued a Notice of Proposed Rule Making on September 29, 2017, which directed the FERC to exercise its authority to set just and reasonable rates that recognize the “resiliency” value provided by generation plants with certain characteristics, including having 90-days or more of on-site fuel and operating in markets where they do not receive rate base treatment through state ratemaking. Nuclear and coal-fired generation plants would have been most likely to be able to meet the requirements. As proposed, the DOE would value resiliency through rates that recover “compensable costs” that were defined to include the recovery of operating and fuel expenses, debt service and a fair return on equity. On January 8, 2018, the FERC issued an order terminating this docket stating that it failed to satisfy the legal requirements of Section 206 of the Federal Power Act of 1935. The FERC initiated a new docket to take additional steps to explore resilience issues in RTOs/ISOs. The goal of this new proceeding is to: (1) develop a common understanding among the FERC, State Commissions, RTOs/ISOs, transmission owners, and others as to what resilience of the bulk power system means and requires; (2) understand how each RTO and ISO assesses resilience in its geographic footprint; and (3) use this information to evaluate whether additional action regarding resilience is appropriate at this time. It is not possible to predict the impact of this proceeding on our business, financial condition or results of operations. FAC and Authorized Annual Jurisdictional Net Operating Income IPL may apply to the IURC for a change in IPL’s fuel charge every three months to recover IPL’s estimated fuel costs, including the energy portion of purchased power costs, which may be above or below the levels included in IPL’s basic rates and charges. IPL must present evidence in each FAC proceeding that it has made every reasonable effort to acquire fuel and generate or purchase power or both so as to provide electricity to its retail customers at the lowest fuel cost reasonably possible. Independent of the IURC’s ability to review basic rates and charges, Indiana law requires electric utilities under the jurisdiction of the IURC to meet operating expense and income test requirements as a condition for approval of requested changes in the FAC. Additionally, customer refunds may result if a utility’s rolling twelve-month operating income, determined at quarterly measurement dates, exceeds a utility’s authorized annual jurisdictional net operating income and there are not sufficient applicable cumulative net operating income deficiencies against which the excess rolling twelve-month jurisdictional net operating income can be offset. ECCRA IPL may apply to the IURC for approval of a rate adjustment known as the ECCRA every six months to recover costs (including a return) to comply with certain environmental regulations applicable to IPL’s generating stations. The total amount of IPL’s equipment approved for ECCRA recovery as of December 31, 2017 was $772 million. The jurisdictional revenue requirement that was approved by the IURC to be included in IPL’s rates for the six-month period from September 2017 through February 2018 was $48.0 million. During the years ended December 31, 2017, 2016 and 2015, we made environmental compliance expenditures of $59.1 million, $158.9 million, and $252.6 million, respectively. The vast majority of such costs are recoverable through our ECCRA filings. DSM In December 2014, we received approval from the IURC of our 2015-2016 DSM plan. The approval included cost recovery on a set of DSM programs to be offered in 2015-2016 that was similar to the 2014 set of programs. It also included the ability for us to receive performance incentives dependent upon the level of success of the programs. Additionally, we were granted authority to record a regulatory asset for recovery in a future base rate case proceeding for lost margins which result from decreased kWh related to implementation of these DSM programs. We began recovering lost margins in the second half of 2016 utilizing the cost of service allocations approved in the IURC’s March 2016 rate case order. In December 2016, we received approval from the IURC of our DSM programs through the end of 2017; however, the IURC denied shareholder incentives pursuant to this order. IPL received shareholder incentives of approximately $10.7 million in 2016. On February 7, 2018, the IURC approved a settlement agreement establishing a new three year DSM plan for IPL through 2020. The approval included cost recovery of programs as well as performance incentives, depending on the level of success of the programs. The order also approved recovery of lost revenues, consistent with the provisions of the settlement agreement. Wind and Solar Power Purchase Agreements We are committed under a power purchase agreement to purchase all wind-generated electricity through 2029 from a wind project in Indiana. We are also committed under another agreement to purchase all wind-generated electricity through 2031 from a project in Minnesota. The Indiana project has a maximum output capacity of approximately 100 MW and the Minnesota project has a maximum output capacity of approximately 200 MW. In addition, we have 97 MW of solar-generated electricity in our service territory under long-term contracts in 2018 (these long-term contracts expire ranging from 2021 to 2032), of which 95 MW was in operation as of December 31, 2017. We have authority from the IURC to recover the costs for all of these agreements through an adjustment mechanism administered within the FAC. If and when IPL sells the renewable energy attributes (in the form of renewable energy credits) generated from these facilities, the proceeds are passed back to IPL’s retail customers through the FAC. Taxes On January 3, 2018, the IURC opened a generic investigation to review and consider the impacts from the TCJA and how any resulting benefits should be realized by customers. The IURC’s order opening this investigation directed Indiana utilities to apply regulatory accounting treatment, such as the use of regulatory assets and regulatory liabilities, for all estimated impacts resulting from the TCJA. On February 16, 2018, the IURC issued an order establishing two phases of the investigation. The first phase directs respondent utilities (including IPL) to make a filing by March 25, 2018 to adjust respondents’ rates and charges for service, the impact of a lower federal income tax rate. The IURC will hold an attorney’s conference on May 3, 2018 to establish the phase two procedural schedule to discuss the remaining issues from the TCJA, including treatment of deferred taxes and how these benefits will be realized by customers. The Company is reviewing the IURC’s initial order and the ultimate result of the generic investigation cannot be determined at this time, although it could be material. See also Note 8, “Income Taxes” for further information.
Indianapolis Power And Light Company [Member]
Entity Information [Line Items]
Regulatory Matters	. REGULATORY MATTERS General IPL is subject to regulation by the IURC as to its services and facilities, the valuation of property, the construction, purchase, or lease of electric generating facilities, the classification of accounts, rates of depreciation, retail rates and charges, the issuance of securities (other than evidences of indebtedness payable less than twelve months after the date of issue), the acquisition and sale of some public utility properties or securities and certain other matters. In addition, IPL is subject to the jurisdiction of the FERC with respect to, among other things, short-term borrowings not regulated by the IURC, the sale of electricity at wholesale, the transmission of electric energy in interstate commerce, the classification of accounts, reliability standards, and the acquisition and sale of utility property in certain circumstances as provided by the Federal Power Act. As a regulated entity, IPL is required to use certain accounting methods prescribed by regulatory bodies which may differ from those accounting methods required to be used by unregulated entities. IPL is also affected by the regulatory jurisdiction of the EPA at the federal level, and the IDEM at the state level. Other significant regulatory agencies affecting IPL include, but are not limited to, the NERC, the U.S. Department of Labor and the IOSHA. Basic Rates and Charges IPL’s basic rates and charges represent the largest component of its annual revenues. IPL’s basic rates and charges are determined after giving consideration, on a pro-forma basis, to all allowable costs for ratemaking purposes including a fair return on the fair value of the utility property used and useful in providing service to customers. These basic rates and charges are set and approved by the IURC after public hearings. Such proceedings, which have occurred at irregular intervals, involve IPL, the IURC, the Indiana Office of Utility Consumer Counselor, and other interested stakeholders. Pursuant to statute, the IURC is to conduct a periodic review of the basic rates and charges of all Indiana utilities at least once every four years, but the IURC has the authority to review the rates of any Indiana utility at any time. Once set, the basic rates and charges authorized do not assure the realization of a fair return on the fair value of property. IPL’s declining block rate structure generally provides for residential and commercial customers to be charged a lower per kWh rate at higher consumption levels. Therefore, as volumes increase, the weighted average price per kWh decreases. Numerous factors including, but not limited to, weather, inflation, customer growth and usage, the level of actual operating and maintenance expenditures, capital expenditures including those required by environmental regulations, fuel costs, and generating unit availability, can affect the return realized. In May 2014, IPL received an order from the IURC granting approval to build a 644 to 685 MW CCGT at Eagle Valley. The costs to build and operate the CCGT, other than fuel costs, will not be recoverable by IPL through rates until the conclusion of a base rate case proceeding with the IURC after construction is completed. The CCGT was originally expected to be completed in the first half of 2017 and that timing was changed in 2017 to an expected completion in the first half of 2018. IPL filed a petition with the IURC on December 21, 2017, for authority to increase its basic rates and charges to coincide with the expected completion of the CCGT in the first half of 2018. IPL’s proposed revenue increase was $124.5 million annually, or 9.1%. On February 16, 2018, IPL filed an update to such petition to reflect the federal income tax law changes passed, which reduced the revenue increase IPL is seeking to $96.7 million, or7.1%. An order on this proceeding will likely be issued by the IURC by the first quarter of 2019. In March 2016, the IURC issued the 2016 Rate Order authorizing IPL to increase its basic rates and charges by $30.8 million annually. The order also authorized IPL to collect, over a ten year period, $117.7 million of previously deferred regulatory assets related to IPL’s participation in the regional transmission organization known as MISO. Such deferred costs are amortized to expense over ten years. Accordingly, $11.8 million of IPL’s long-term MISO regulatory asset is included within current regulatory assets on the accompanying Consolidated Balance Sheets. The rate order also authorized an increase in IPL’s depreciation rates of $24.3 million annually compared to the twelve months ended June 30, 2014, which is the period upon which the rate increase was calculated. IPL also received approval to implement three new rate riders for current recovery from customers of ongoing MISO costs and capacity costs, and for sharing with customers 50% of wholesale sales margins above and below the established benchmark of $6.3 million. Additionally, the capacity rider provides that IPL will share with customers 50% of any capacity sales. The order approved recovery of IPL’s pension expenses and a return on IPL’s discretionary pension fundings. While the IURC noted in the order that they found IPL’s Service Company cost allocations to be reasonable, IPL was directed to request the FERC to review its Service Company allocations. In September 2017, the FERC completed its review, authorizing the Service Company’s allocation of costs of non-power goods and services to IPL. In the 2016 Rate Order, the IURC also closed their investigation into IPL’s underground network. Some of the intervening parties in the IURC rate case filed petitions for reconsideration of the IURC’s March 2016 order with respect to certain issues. These petitions were subsequently denied by the IURC. In addition, certain intervening parties filed notices of appeal of the order. On April 5, 2017, the Indiana Court of Appeals affirmed the IURC’s March 2016 order. CCR On April 26, 2017, the IURC approved IPL’s CCR compliance request to install a bottom ash dewatering system at its Petersburg generating station and to recover 80% of qualifying costs through a rate adjustment mechanism with the remainder recorded as a regulatory asset for recovery in a subsequent rate case. The approved capital cost of the CCR compliance plan is approximately $47 million. IPL’s bottom ash dewatering system at its Petersburg generating station went into service in September 2017. NAAQS On April 26, 2017, the IURC approved IPL’s request for NAAQS SO2 compliance at its Petersburg generation station with 80% of qualifying costs recovered through a rate adjustment mechanism and the remainder recorded as a regulatory asset for recovery in a subsequent rate case. The approved capital cost of the NAAQS SO2 compliance plan is approximately $29 million. This project is expected to be fully in service in the first quarter of 2019. Other The DOE issued a Notice of Proposed Rule Making on September 29, 2017, which directed the FERC to exercise its authority to set just and reasonable rates that recognize the “resiliency” value provided by generation plants with certain characteristics, including having 90-days or more of on-site fuel and operating in markets where they do not receive rate base treatment through state ratemaking. Nuclear and coal-fired generation plants would have been most likely to be able to meet the requirements. As proposed, the DOE would value resiliency through rates that recover “compensable costs” that were defined to include the recovery of operating and fuel expenses, debt service and a fair return on equity. On January 8, 2018, the FERC issued an order terminating this docket stating that it failed to satisfy the legal requirements of Section 206 of the Federal Power Act of 1935. The FERC initiated a new docket to take additional steps to explore resilience issues in RTOs/ISOs. The goal of this new proceeding is to: (1) develop a common understanding among the FERC, State Commissions, RTOs/ISOs, transmission owners, and others as to what resilience of the bulk power system means and requires; (2) understand how each RTO and ISO assesses resilience in its geographic footprint; and (3) use this information to evaluate whether additional action regarding resilience is appropriate at this time. It is not possible to predict the impact of this proceeding on our business, financial condition or results of operations. FAC and Authorized Annual Jurisdictional Net Operating Income IPL may apply to the IURC for a change in IPL’s fuel charge every three months to recover IPL’s estimated fuel costs, including the energy portion of purchased power costs, which may be above or below the levels included in IPL’s basic rates and charges. IPL must present evidence in each FAC proceeding that it has made every reasonable effort to acquire fuel and generate or purchase power or both so as to provide electricity to its retail customers at the lowest fuel cost reasonably possible. Independent of the IURC’s ability to review basic rates and charges, Indiana law requires electric utilities under the jurisdiction of the IURC to meet operating expense and income test requirements as a condition for approval of requested changes in the FAC. Additionally, customer refunds may result if a utility’s rolling twelve-month operating income, determined at quarterly measurement dates, exceeds a utility’s authorized annual jurisdictional net operating income and there are not sufficient applicable cumulative net operating income deficiencies against which the excess rolling twelve-month jurisdictional net operating income can be offset. ECCRA IPL may apply to the IURC for approval of a rate adjustment known as the ECCRA every six months to recover costs (including a return) to comply with certain environmental regulations applicable to IPL’s generating stations. The total amount of IPL’s equipment approved for ECCRA recovery as of December 31, 2017 was $772 million. The jurisdictional revenue requirement that was approved by the IURC to be included in IPL’s rates for the six-month period from September 2017 through February 2018 was $48.0 million. During the years ended December 31, 2017, 2016 and 2015, we made environmental compliance expenditures of $59.1 million, $158.9 million, and $252.6 million, respectively. The vast majority of such costs are recoverable through IPL’s ECCRA filings. DSM In December 2014, IPL received approval from the IURC of its 2015-2016 DSM plan. The approval included cost recovery on a set of DSM programs to be offered in 2015-2016 that was similar to the 2014 set of programs. It also included the ability for IPL to receive performance incentives dependent upon the level of success of the programs. Additionally, IPL was granted authority to record a regulatory asset for recovery in a future base rate case proceeding for lost margins which result from decreased kWh related to implementation of these DSM programs. IPL began recovering lost margins in the second half of 2016 utilizing the cost of service allocations approved in the IURC’s March 2016 rate case order. In December 2016, IPL received approval from the IURC of its DSM programs through the end of 2017; however, the IURC denied shareholder incentives pursuant to this order. IPL received shareholder incentives of approximately $10.7 million in 2016. On February 7, 2018, the IURC approved a settlement agreement establishing a new three year DSM plan for IPL through 2020. The approval included cost recovery of programs as well as performance incentives, depending on the level of success of the programs. The order also approved recovery of lost revenues, consistent with the provisions of the settlement agreement. Wind and Solar Power Purchase Agreements IPL is committed under a power purchase agreement to purchase all wind-generated electricity through 2029 from a wind project in Indiana. IPL is also committed under another agreement to purchase all wind-generated electricity through 2031 from a project in Minnesota. The Indiana project has a maximum output capacity of approximately 100 MW and the Minnesota project has a maximum output capacity of approximately 200 MW. In addition, IPL has 97 MW of solar-generated electricity in its service territory under long-term contracts in 2018 (these long-term contracts expire ranging from 2021 to 2032), of which 95 MW was in operation as of December 31, 2017. IPL has authority from the IURC to recover the costs for all of these agreements through an adjustment mechanism administered within the FAC. If and when IPL sells the renewable energy attributes (in the form of renewable energy credits) generated from these facilities, the proceeds are passed back to IPL’s retail customers through the FAC. Taxes On January 3, 2018, the IURC opened a generic investigation to review and consider the impacts from the TCJA and how any resulting benefits should be realized by customers. The IURC’s order opening this investigation directed Indiana utilities to apply regulatory accounting treatment, such as the use of regulatory assets and regulatory liabilities, for all estimated impacts resulting from the TCJA. On February 16, 2018, the IURC issued an order establishing two phases of the investigation. The first phase directs respondent utilities (including IPL) to make a filing by March 25, 2018 to adjust respondents’ rates and charges for service, the impact of a lower federal income tax rate. The IURC will hold an attorney’s conference on May 3, 2018 to establish the phase two procedural schedule to discuss the remaining issues from the TCJA, including treatment of deferred taxes and how these benefits will be realized by customers. IPL is reviewing the IURC’s initial order and the ultimate result of the generic investigation cannot be determined at this time, although it could be material. See also Note 8, “Income Taxes” for further information.