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Summary Of Significant Accounting Policies (Policy) | 9 Months Ended
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Sep. 30, 2013
Property, Plant and Equipment [Line Items] |
General, Basis of Accounting | The interim unaudited condensed consolidated financial statements included herein have been prepared by Alliant Energy, IPL and WPL pursuant to the rules and regulations of the SEC. Accordingly, certain information and note disclosures normally included in financial statements prepared in accordance with GAAP have been condensed or omitted, although management believes that the disclosures are adequate to make the information presented not misleading. These financial statements should be read in conjunction with the financial statements and the notes thereto included in Alliant Energy’s, IPL’s and WPL’s latest combined Annual Report on Form 10-K.
General, Use of Estimates | In the opinion of management, all adjustments, which unless otherwise noted are normal and recurring in nature, necessary for a fair presentation of the results of operations, financial position and cash flows have been made. Results for the nine months ended September 30, 2013 are not necessarily indicative of results that may be expected for the year ending December 31, 2013. A change in management’s estimates or assumptions could have a material impact on Alliant Energy’s, IPL’s and WPL’s respective financial condition and results of operations during the period in which such change occurred.
General, Reclassification | Certain prior period amounts in the Condensed Consolidated Financial Statements and Combined Notes to Condensed Consolidated Financial Statements have been reclassified to conform to the current period presentation for comparative purposes. Unless otherwise noted, the notes herein have been revised to exclude discontinued operations and assets and liabilities held for sale for all periods presented.
Regulatory Assets and Regulatory Liabilities | Regulatory Assets and Regulatory Liabilities - Regulatory assets were comprised of the following items (in millions):
| Alliant Energy |  | IPL |  | WPL
| September 30, 2013 |  | December 31, 2012 |  | September 30, 2013 |  | December 31, 2012 |  | September 30, 2013 |  | December 31, 2012
Tax-related |  | $813.6 |  |  |  | $770.7 |  |  |  | $783.6 |  |  |  | $746.2 |  |  |  | $30.0 |  |  |  | $24.5 |
Pension and other postretirement benefits costs | 525.2 |  |  | 549.2 |  |  | 267.9 |  |  | 279.3 |  |  | 257.3 |  |  | 269.9 |
AROs | 66.9 |  |  | 62.4 |  |  | 38.8 |  |  | 38.6 |  |  | 28.1 |  |  | 23.8 |
Emission allowances | 30.0 |  |  | 30.0 |  |  | 30.0 |  |  | 30.0 |  |  | — |  |  | — |
Derivatives | 26.8 |  |  | 40.2 |  |  | 6.9 |  |  | 16.3 |  |  | 19.9 |  |  | 23.9 |
Environmental-related costs | 26.0 |  |  | 34.9 |  |  | 21.8 |  |  | 30.3 |  |  | 4.2 |  |  | 4.6 |
Other | 107.7 |  |  | 125.0 |  |  | 67.0 |  |  | 77.2 |  |  | 40.7 |  |  | 47.8 |
|  | $1,596.2 |  |  |  | $1,612.4 |  |  |  | $1,216.0 |  |  |  | $1,217.9 |  |  |  | $380.2 |  |  |  | $394.5 |
Regulatory liabilities were comprised of the following items (in millions):
| Alliant Energy |  | IPL |  | WPL
| September 30, 2013 |  | December 31, 2012 |  | September 30, 2013 |  | December 31, 2012 |  | September 30, 2013 |  | December 31, 2012
Cost of removal obligations |  | $415.7 |  |  |  | $408.7 |  |  |  | $275.8 |  |  |  | $268.0 |  |  |  | $139.9 |  |  |  | $140.7 |
IPL’s tax benefit riders | 288.8 |  |  | 355.8 |  |  | 288.8 |  |  | 355.8 |  |  | — |  |  | — |
Energy conservation cost recovery | 58.1 |  |  | 55.1 |  |  | 12.6 |  |  | 10.0 |  |  | 45.5 |  |  | 45.1 |
IPL’s electric transmission assets sale | 24.3 |  |  | 32.5 |  |  | 24.3 |  |  | 32.5 |  |  | — |  |  | — |
Commodity cost recovery | 7.0 |  |  | 17.7 |  |  | 1.1 |  |  | 5.2 |  |  | 5.9 |  |  | 12.5 |
Other | 43.7 |  |  | 46.3 |  |  | 27.8 |  |  | 29.9 |  |  | 15.9 |  |  | 16.4 |
|  | $837.6 |  |  |  | $916.1 |  |  |  | $630.4 |  |  |  | $701.4 |  |  |  | $207.2 |  |  |  | $214.7 |
Tax-related - Alliant Energy’s and IPL’s tax-related regulatory assets are generally impacted by certain property-related differences at IPL for which deferred tax is not recorded in the income statement pursuant to Iowa rate-making principles. Deferred tax amounts are recorded to regulatory assets, along with the necessary revenue requirement tax gross-ups. During the nine months ended September 30, 2013, Alliant Energy’s and IPL’s tax-related regulatory assets increased primarily due to qualifying repair expenditures at IPL. Derivatives - In accordance with IPL’s and WPL’s fuel and natural gas recovery mechanisms, prudently incurred costs from derivative instruments are recovered from customers in the future after any losses are realized and gains from derivative instruments are refunded to customers in the future after any gains are realized. Based on these recovery mechanisms, the changes in the fair value of derivative liabilities/assets resulted in comparable changes to regulatory assets/liabilities on the Condensed Consolidated Balance Sheets for the nine months ended September 30, 2013. Refer to Note 11 for additional details of derivative assets and derivative liabilities. IPL’s tax benefit riders - Alliant Energy’s and IPL’s “IPL’s tax benefit riders” regulatory liabilities in the above table decreased $67 million during the nine months ended September 30, 2013 due to the following items: Electric tax benefit rider - In January 2011, the IUB approved an electric tax benefit rider proposed by IPL, which utilizes regulatory liabilities to credit bills of Iowa retail electric customers beginning in February 2011 to help offset the impact of rate increases on such customers. These regulatory liabilities are related to tax benefits from tax accounting method changes for repairs expenditures, allocation of mixed service costs and allocation of insurance proceeds from floods in 2008. IPL utilized $59 million of regulatory liabilities to credit Iowa retail electric customers’ bills during the nine months ended September 30, 2013. Gas tax benefit rider - In November 2012, the IUB approved a gas tax benefit rider proposed by IPL, which utilizes regulatory liabilities to credit bills of Iowa retail gas customers beginning in January 2013 to help offset the impact of rate increases on such customers. These regulatory liabilities are related to tax benefits from tax accounting method changes for repairs expenditures, allocation of mixed service costs and allocation of insurance proceeds from floods in 2008. IPL utilized $8 million of regulatory liabilities to credit Iowa retail gas customers’ bills during the nine months ended September 30, 2013. Refer to Note 4 for additional details regarding IPL’s tax benefit riders. Other - Based on the PSCW’s July 2012 order related to WPL’s 2013/2014 test period Wisconsin retail electric and gas rate case, WPL was authorized to recover previously incurred costs associated with the acquisition of a 25% ownership interest in Edgewater Unit 5 and proposed clean air compliance plan projects. As a result, Alliant Energy and WPL recorded a $5 million increase to regulatory assets, and a $5 million credit to “Utility - Other operation and maintenance” in their Condensed Consolidated Statements of Income during the nine months ended September 30, 2012.
Utility Property, Plant and Equipment | Utility Property, Plant and Equipment - Proposed Sales of IPL’s Minnesota Electric and Natural Gas Distribution Assets - In September 2013, IPL signed a definitive agreement to sell its Minnesota electric distribution assets to Southern Minnesota Energy Cooperative, a combined group of various neighboring electric cooperatives. Also in September 2013, IPL signed a definitive agreement to sell its Minnesota natural gas distribution assets to Minnesota Energy Resources Corporation, a subsidiary of Integrys Energy Group, Inc. Proceeds from the sales are expected to be approximately $128 million in aggregate, subject to customary closing adjustments. The proceeds are expected to reduce Alliant Energy’s and IPL’s financing requirements. Pending all necessary federal and state regulatory approvals, including the MPUC, FERC and the IUB, the transactions are expected to be concluded in the second half of 2014. The sales price of the assets expected to be sold, which primarily consist of property, plant and equipment, and working capital items, is expected to result in a modest gain. Any after-tax gain realized from the transaction may be subject to refund to IPL’s customers. As of September 30, 2013, IPL’s assets and liabilities included in the sale agreements did not meet the criteria to be classified as held for sale due to uncertainties in the regulatory approval process. The operating results of IPL’s Minnesota electric and natural gas distribution businesses did not qualify as discontinued operations as of September 30, 2013. The electric distribution asset sales agreement includes a wholesale power supply agreement between IPL and Southern Minnesota Energy Cooperative, which is subject to FERC approval. The agreement contains a five-year termination notice, which may not be given until the fifth anniversary of the effective date of the agreement, resulting in a minimum term of 10 years. The agreement remains in effect unless notice to terminate is provided by either party. This wholesale power supply agreement includes standardized pricing mechanisms that are detailed in IPL’s current tariffs accepted by FERC through wholesale rate case proceedings. The tariffs include an annual true-up process for actual costs incurred. IPL’s current return on common equity authorized by FERC related to its wholesale electric rates is 10.97%. As a result of IPL’s requirement to supply electricity to Southern Minnesota Energy Cooperative under the wholesale power supply agreement, the sale of the electric distribution assets is not expected to have a significant impact on IPL’s current generation plans.
Comprehensive Income | Comprehensive Income - For the three and nine months ended September 30, 2013 and 2012, Alliant Energy had no other comprehensive income; therefore, its comprehensive income was equal to its net income and its comprehensive income attributable to Alliant Energy common shareowners was equal to its net income attributable to Alliant Energy common shareowners for such periods. For the three and nine months ended September 30, 2013 and 2012, IPL and WPL had no other comprehensive income; therefore, their comprehensive income was equal to their net income and their comprehensive income available for common stock was equal to their earnings available for common stock for such periods.
IPL [Member] |
Property, Plant and Equipment [Line Items] |
General, Basis of Accounting | The interim unaudited condensed consolidated financial statements included herein have been prepared by Alliant Energy, IPL and WPL pursuant to the rules and regulations of the SEC. Accordingly, certain information and note disclosures normally included in financial statements prepared in accordance with GAAP have been condensed or omitted, although management believes that the disclosures are adequate to make the information presented not misleading. These financial statements should be read in conjunction with the financial statements and the notes thereto included in Alliant Energy’s, IPL’s and WPL’s latest combined Annual Report on Form 10-K.
General, Use of Estimates | In the opinion of management, all adjustments, which unless otherwise noted are normal and recurring in nature, necessary for a fair presentation of the results of operations, financial position and cash flows have been made. Results for the nine months ended September 30, 2013 are not necessarily indicative of results that may be expected for the year ending December 31, 2013. A change in management’s estimates or assumptions could have a material impact on Alliant Energy’s, IPL’s and WPL’s respective financial condition and results of operations during the period in which such change occurred.
General, Reclassification | Certain prior period amounts in the Condensed Consolidated Financial Statements and Combined Notes to Condensed Consolidated Financial Statements have been reclassified to conform to the current period presentation for comparative purposes. Unless otherwise noted, the notes herein have been revised to exclude discontinued operations and assets and liabilities held for sale for all periods presented.
Regulatory Assets and Regulatory Liabilities | Regulatory Assets and Regulatory Liabilities - Regulatory assets were comprised of the following items (in millions):
| Alliant Energy |  | IPL |  | WPL
| September 30, 2013 |  | December 31, 2012 |  | September 30, 2013 |  | December 31, 2012 |  | September 30, 2013 |  | December 31, 2012
Tax-related |  | $813.6 |  |  |  | $770.7 |  |  |  | $783.6 |  |  |  | $746.2 |  |  |  | $30.0 |  |  |  | $24.5 |
Pension and other postretirement benefits costs | 525.2 |  |  | 549.2 |  |  | 267.9 |  |  | 279.3 |  |  | 257.3 |  |  | 269.9 |
AROs | 66.9 |  |  | 62.4 |  |  | 38.8 |  |  | 38.6 |  |  | 28.1 |  |  | 23.8 |
Emission allowances | 30.0 |  |  | 30.0 |  |  | 30.0 |  |  | 30.0 |  |  | — |  |  | — |
Derivatives | 26.8 |  |  | 40.2 |  |  | 6.9 |  |  | 16.3 |  |  | 19.9 |  |  | 23.9 |
Environmental-related costs | 26.0 |  |  | 34.9 |  |  | 21.8 |  |  | 30.3 |  |  | 4.2 |  |  | 4.6 |
Other | 107.7 |  |  | 125.0 |  |  | 67.0 |  |  | 77.2 |  |  | 40.7 |  |  | 47.8 |
|  | $1,596.2 |  |  |  | $1,612.4 |  |  |  | $1,216.0 |  |  |  | $1,217.9 |  |  |  | $380.2 |  |  |  | $394.5 |
Regulatory liabilities were comprised of the following items (in millions):
| Alliant Energy |  | IPL |  | WPL
| September 30, 2013 |  | December 31, 2012 |  | September 30, 2013 |  | December 31, 2012 |  | September 30, 2013 |  | December 31, 2012
Cost of removal obligations |  | $415.7 |  |  |  | $408.7 |  |  |  | $275.8 |  |  |  | $268.0 |  |  |  | $139.9 |  |  |  | $140.7 |
IPL’s tax benefit riders | 288.8 |  |  | 355.8 |  |  | 288.8 |  |  | 355.8 |  |  | — |  |  | — |
Energy conservation cost recovery | 58.1 |  |  | 55.1 |  |  | 12.6 |  |  | 10.0 |  |  | 45.5 |  |  | 45.1 |
IPL’s electric transmission assets sale | 24.3 |  |  | 32.5 |  |  | 24.3 |  |  | 32.5 |  |  | — |  |  | — |
Commodity cost recovery | 7.0 |  |  | 17.7 |  |  | 1.1 |  |  | 5.2 |  |  | 5.9 |  |  | 12.5 |
Other | 43.7 |  |  | 46.3 |  |  | 27.8 |  |  | 29.9 |  |  | 15.9 |  |  | 16.4 |
|  | $837.6 |  |  |  | $916.1 |  |  |  | $630.4 |  |  |  | $701.4 |  |  |  | $207.2 |  |  |  | $214.7 |
Tax-related - Alliant Energy’s and IPL’s tax-related regulatory assets are generally impacted by certain property-related differences at IPL for which deferred tax is not recorded in the income statement pursuant to Iowa rate-making principles. Deferred tax amounts are recorded to regulatory assets, along with the necessary revenue requirement tax gross-ups. During the nine months ended September 30, 2013, Alliant Energy’s and IPL’s tax-related regulatory assets increased primarily due to qualifying repair expenditures at IPL. Derivatives - In accordance with IPL’s and WPL’s fuel and natural gas recovery mechanisms, prudently incurred costs from derivative instruments are recovered from customers in the future after any losses are realized and gains from derivative instruments are refunded to customers in the future after any gains are realized. Based on these recovery mechanisms, the changes in the fair value of derivative liabilities/assets resulted in comparable changes to regulatory assets/liabilities on the Condensed Consolidated Balance Sheets for the nine months ended September 30, 2013. Refer to Note 11 for additional details of derivative assets and derivative liabilities. IPL’s tax benefit riders - Alliant Energy’s and IPL’s “IPL’s tax benefit riders” regulatory liabilities in the above table decreased $67 million during the nine months ended September 30, 2013 due to the following items: Electric tax benefit rider - In January 2011, the IUB approved an electric tax benefit rider proposed by IPL, which utilizes regulatory liabilities to credit bills of Iowa retail electric customers beginning in February 2011 to help offset the impact of rate increases on such customers. These regulatory liabilities are related to tax benefits from tax accounting method changes for repairs expenditures, allocation of mixed service costs and allocation of insurance proceeds from floods in 2008. IPL utilized $59 million of regulatory liabilities to credit Iowa retail electric customers’ bills during the nine months ended September 30, 2013. Gas tax benefit rider - In November 2012, the IUB approved a gas tax benefit rider proposed by IPL, which utilizes regulatory liabilities to credit bills of Iowa retail gas customers beginning in January 2013 to help offset the impact of rate increases on such customers. These regulatory liabilities are related to tax benefits from tax accounting method changes for repairs expenditures, allocation of mixed service costs and allocation of insurance proceeds from floods in 2008. IPL utilized $8 million of regulatory liabilities to credit Iowa retail gas customers’ bills during the nine months ended September 30, 2013. Refer to Note 4 for additional details regarding IPL’s tax benefit riders. Other - Based on the PSCW’s July 2012 order related to WPL’s 2013/2014 test period Wisconsin retail electric and gas rate case, WPL was authorized to recover previously incurred costs associated with the acquisition of a 25% ownership interest in Edgewater Unit 5 and proposed clean air compliance plan projects. As a result, Alliant Energy and WPL recorded a $5 million increase to regulatory assets, and a $5 million credit to “Utility - Other operation and maintenance” in their Condensed Consolidated Statements of Income during the nine months ended September 30, 2012.
Utility Property, Plant and Equipment | Utility Property, Plant and Equipment - Proposed Sales of IPL’s Minnesota Electric and Natural Gas Distribution Assets - In September 2013, IPL signed a definitive agreement to sell its Minnesota electric distribution assets to Southern Minnesota Energy Cooperative, a combined group of various neighboring electric cooperatives. Also in September 2013, IPL signed a definitive agreement to sell its Minnesota natural gas distribution assets to Minnesota Energy Resources Corporation, a subsidiary of Integrys Energy Group, Inc. Proceeds from the sales are expected to be approximately $128 million in aggregate, subject to customary closing adjustments. The proceeds are expected to reduce Alliant Energy’s and IPL’s financing requirements. Pending all necessary federal and state regulatory approvals, including the MPUC, FERC and the IUB, the transactions are expected to be concluded in the second half of 2014. The sales price of the assets expected to be sold, which primarily consist of property, plant and equipment, and working capital items, is expected to result in a modest gain. Any after-tax gain realized from the transaction may be subject to refund to IPL’s customers. As of September 30, 2013, IPL’s assets and liabilities included in the sale agreements did not meet the criteria to be classified as held for sale due to uncertainties in the regulatory approval process. The operating results of IPL’s Minnesota electric and natural gas distribution businesses did not qualify as discontinued operations as of September 30, 2013. The electric distribution asset sales agreement includes a wholesale power supply agreement between IPL and Southern Minnesota Energy Cooperative, which is subject to FERC approval. The agreement contains a five-year termination notice, which may not be given until the fifth anniversary of the effective date of the agreement, resulting in a minimum term of 10 years. The agreement remains in effect unless notice to terminate is provided by either party. This wholesale power supply agreement includes standardized pricing mechanisms that are detailed in IPL’s current tariffs accepted by FERC through wholesale rate case proceedings. The tariffs include an annual true-up process for actual costs incurred. IPL’s current return on common equity authorized by FERC related to its wholesale electric rates is 10.97%. As a result of IPL’s requirement to supply electricity to Southern Minnesota Energy Cooperative under the wholesale power supply agreement, the sale of the electric distribution assets is not expected to have a significant impact on IPL’s current generation plans.
Comprehensive Income | Comprehensive Income - For the three and nine months ended September 30, 2013 and 2012, Alliant Energy had no other comprehensive income; therefore, its comprehensive income was equal to its net income and its comprehensive income attributable to Alliant Energy common shareowners was equal to its net income attributable to Alliant Energy common shareowners for such periods. For the three and nine months ended September 30, 2013 and 2012, IPL and WPL had no other comprehensive income; therefore, their comprehensive income was equal to their net income and their comprehensive income available for common stock was equal to their earnings available for common stock for such periods.
WPL [Member] |
Property, Plant and Equipment [Line Items] |
General, Basis of Accounting | The interim unaudited condensed consolidated financial statements included herein have been prepared by Alliant Energy, IPL and WPL pursuant to the rules and regulations of the SEC. Accordingly, certain information and note disclosures normally included in financial statements prepared in accordance with GAAP have been condensed or omitted, although management believes that the disclosures are adequate to make the information presented not misleading. These financial statements should be read in conjunction with the financial statements and the notes thereto included in Alliant Energy’s, IPL’s and WPL’s latest combined Annual Report on Form 10-K.
General, Use of Estimates | In the opinion of management, all adjustments, which unless otherwise noted are normal and recurring in nature, necessary for a fair presentation of the results of operations, financial position and cash flows have been made. Results for the nine months ended September 30, 2013 are not necessarily indicative of results that may be expected for the year ending December 31, 2013. A change in management’s estimates or assumptions could have a material impact on Alliant Energy’s, IPL’s and WPL’s respective financial condition and results of operations during the period in which such change occurred.
General, Reclassification | Certain prior period amounts in the Condensed Consolidated Financial Statements and Combined Notes to Condensed Consolidated Financial Statements have been reclassified to conform to the current period presentation for comparative purposes. Unless otherwise noted, the notes herein have been revised to exclude discontinued operations and assets and liabilities held for sale for all periods presented.
Regulatory Assets and Regulatory Liabilities | Regulatory Assets and Regulatory Liabilities - Regulatory assets were comprised of the following items (in millions):
| Alliant Energy |  | IPL |  | WPL
| September 30, 2013 |  | December 31, 2012 |  | September 30, 2013 |  | December 31, 2012 |  | September 30, 2013 |  | December 31, 2012
Tax-related |  | $813.6 |  |  |  | $770.7 |  |  |  | $783.6 |  |  |  | $746.2 |  |  |  | $30.0 |  |  |  | $24.5 |
Pension and other postretirement benefits costs | 525.2 |  |  | 549.2 |  |  | 267.9 |  |  | 279.3 |  |  | 257.3 |  |  | 269.9 |
AROs | 66.9 |  |  | 62.4 |  |  | 38.8 |  |  | 38.6 |  |  | 28.1 |  |  | 23.8 |
Emission allowances | 30.0 |  |  | 30.0 |  |  | 30.0 |  |  | 30.0 |  |  | — |  |  | — |
Derivatives | 26.8 |  |  | 40.2 |  |  | 6.9 |  |  | 16.3 |  |  | 19.9 |  |  | 23.9 |
Environmental-related costs | 26.0 |  |  | 34.9 |  |  | 21.8 |  |  | 30.3 |  |  | 4.2 |  |  | 4.6 |
Other | 107.7 |  |  | 125.0 |  |  | 67.0 |  |  | 77.2 |  |  | 40.7 |  |  | 47.8 |
|  | $1,596.2 |  |  |  | $1,612.4 |  |  |  | $1,216.0 |  |  |  | $1,217.9 |  |  |  | $380.2 |  |  |  | $394.5 |
Regulatory liabilities were comprised of the following items (in millions):
| Alliant Energy |  | IPL |  | WPL
| September 30, 2013 |  | December 31, 2012 |  | September 30, 2013 |  | December 31, 2012 |  | September 30, 2013 |  | December 31, 2012
Cost of removal obligations |  | $415.7 |  |  |  | $408.7 |  |  |  | $275.8 |  |  |  | $268.0 |  |  |  | $139.9 |  |  |  | $140.7 |
IPL’s tax benefit riders | 288.8 |  |  | 355.8 |  |  | 288.8 |  |  | 355.8 |  |  | — |  |  | — |
Energy conservation cost recovery | 58.1 |  |  | 55.1 |  |  | 12.6 |  |  | 10.0 |  |  | 45.5 |  |  | 45.1 |
IPL’s electric transmission assets sale | 24.3 |  |  | 32.5 |  |  | 24.3 |  |  | 32.5 |  |  | — |  |  | — |
Commodity cost recovery | 7.0 |  |  | 17.7 |  |  | 1.1 |  |  | 5.2 |  |  | 5.9 |  |  | 12.5 |
Other | 43.7 |  |  | 46.3 |  |  | 27.8 |  |  | 29.9 |  |  | 15.9 |  |  | 16.4 |
|  | $837.6 |  |  |  | $916.1 |  |  |  | $630.4 |  |  |  | $701.4 |  |  |  | $207.2 |  |  |  | $214.7 |
Tax-related - Alliant Energy’s and IPL’s tax-related regulatory assets are generally impacted by certain property-related differences at IPL for which deferred tax is not recorded in the income statement pursuant to Iowa rate-making principles. Deferred tax amounts are recorded to regulatory assets, along with the necessary revenue requirement tax gross-ups. During the nine months ended September 30, 2013, Alliant Energy’s and IPL’s tax-related regulatory assets increased primarily due to qualifying repair expenditures at IPL. Derivatives - In accordance with IPL’s and WPL’s fuel and natural gas recovery mechanisms, prudently incurred costs from derivative instruments are recovered from customers in the future after any losses are realized and gains from derivative instruments are refunded to customers in the future after any gains are realized. Based on these recovery mechanisms, the changes in the fair value of derivative liabilities/assets resulted in comparable changes to regulatory assets/liabilities on the Condensed Consolidated Balance Sheets for the nine months ended September 30, 2013. Refer to Note 11 for additional details of derivative assets and derivative liabilities. IPL’s tax benefit riders - Alliant Energy’s and IPL’s “IPL’s tax benefit riders” regulatory liabilities in the above table decreased $67 million during the nine months ended September 30, 2013 due to the following items: Electric tax benefit rider - In January 2011, the IUB approved an electric tax benefit rider proposed by IPL, which utilizes regulatory liabilities to credit bills of Iowa retail electric customers beginning in February 2011 to help offset the impact of rate increases on such customers. These regulatory liabilities are related to tax benefits from tax accounting method changes for repairs expenditures, allocation of mixed service costs and allocation of insurance proceeds from floods in 2008. IPL utilized $59 million of regulatory liabilities to credit Iowa retail electric customers’ bills during the nine months ended September 30, 2013. Gas tax benefit rider - In November 2012, the IUB approved a gas tax benefit rider proposed by IPL, which utilizes regulatory liabilities to credit bills of Iowa retail gas customers beginning in January 2013 to help offset the impact of rate increases on such customers. These regulatory liabilities are related to tax benefits from tax accounting method changes for repairs expenditures, allocation of mixed service costs and allocation of insurance proceeds from floods in 2008. IPL utilized $8 million of regulatory liabilities to credit Iowa retail gas customers’ bills during the nine months ended September 30, 2013. Refer to Note 4 for additional details regarding IPL’s tax benefit riders. Other - Based on the PSCW’s July 2012 order related to WPL’s 2013/2014 test period Wisconsin retail electric and gas rate case, WPL was authorized to recover previously incurred costs associated with the acquisition of a 25% ownership interest in Edgewater Unit 5 and proposed clean air compliance plan projects. As a result, Alliant Energy and WPL recorded a $5 million increase to regulatory assets, and a $5 million credit to “Utility - Other operation and maintenance” in their Condensed Consolidated Statements of Income during the nine months ended September 30, 2012.
Comprehensive Income | Comprehensive Income - For the three and nine months ended September 30, 2013 and 2012, Alliant Energy had no other comprehensive income; therefore, its comprehensive income was equal to its net income and its comprehensive income attributable to Alliant Energy common shareowners was equal to its net income attributable to Alliant Energy common shareowners for such periods. For the three and nine months ended September 30, 2013 and 2012, IPL and WPL had no other comprehensive income; therefore, their comprehensive income was equal to their net income and their comprehensive income available for common stock was equal to their earnings available for common stock for such periods.

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- Definition Disclosure of accounting policy for property, plant and equipment which may include the basis of such assets, depreciation methods used and estimated useful lives, the entity's capitalization policy, including its accounting treatment for costs incurred for repairs and maintenance activities, whether such asset balances include capitalized interest and the method by which such is calculated, how disposals of such assets are accounted for and how impairment of such assets is assessed and recognized. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 235 -SubTopic 10 -Section 50 -Paragraph 3 -URI http://asc.fasb.org/extlink&oid=6367646&loc=d3e18780-107790 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 360 -SubTopic 10 -URI http://asc.fasb.org/subtopic&trid=2155824 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher AICPA -Name Accounting Principles Board Opinion (APB) -Number 22 -Paragraph 12, 13 -LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy. Reference 4: http://www.xbrl.org/2003/role/presentationRef -Publisher AICPA -Name Accounting Research Bulletin (ARB) -Number 43 -Section C -Paragraph 5 -Chapter 9 -LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy. Reference 5: http://www.xbrl.org/2003/role/presentationRef -Publisher AICPA -Name Accounting Principles Board Opinion (APB) -Number 12 -Paragraph 5 -Subparagraph d -LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy. Reference 6: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 144 -Paragraph 7 -LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy. Reference 7: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02.13(a)) -URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682 Reference 8: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 02 -Paragraph 13 -Subparagraph a -Article 5 Reference 9: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 34 -Paragraph 8, 9 -LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy. + Details
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