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Regulatory Matters | 3 Months Ended
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Mar. 31, 2016
Public Utilities, General Disclosures [Line Items] |
Regulatory Matters | REGULATORY MATTERS Regulatory Assets and Regulatory Liabilities - Regulatory assets were comprised of the following items (in millions):
| Alliant Energy |  | IPL |  | WPL
| March 31, 2016 |  | December 31, 2015 |  | March 31, 2016 |  | December 31, 2015 |  | March 31, 2016 |  | December 31, 2015
Tax-related |  | $1,002.7 |  |  |  | $987.7 |  |  |  | $972.0 |  |  |  | $958.2 |  |  |  | $30.7 |  |  |  | $29.5 |
Pension and OPEB costs | 570.0 |  |  | 579.5 |  |  | 293.6 |  |  | 298.1 |  |  | 276.4 |  |  | 281.4 |
AROs | 96.1 |  |  | 92.4 |  |  | 54.1 |  |  | 50.8 |  |  | 42.0 |  |  | 41.6 |
Derivatives | 86.6 |  |  | 70.6 |  |  | 25.5 |  |  | 28.2 |  |  | 61.1 |  |  | 42.4 |
WPL’s EGUs retired early | 43.2 |  |  | 45.0 |  |  | — |  |  | — |  |  | 43.2 |  |  | 45.0 |
Emission allowances | 26.7 |  |  | 26.9 |  |  | 26.7 |  |  | 26.9 |  |  | — |  |  | — |
Commodity cost recovery | 26.3 |  |  | 35.9 |  |  | 0.3 |  |  | 2.8 |  |  | 26.0 |  |  | 33.1 |
Other | 65.6 |  |  | 70.6 |  |  | 33.7 |  |  | 37.6 |  |  | 31.9 |  |  | 33.0 |
|  | $1,917.2 |  |  |  | $1,908.6 |  |  |  | $1,405.9 |  |  |  | $1,402.6 |  |  |  | $511.3 |  |  |  | $506.0 |
Regulatory liabilities were comprised of the following items (in millions):
| Alliant Energy |  | IPL |  | WPL
| March 31, 2016 |  | December 31, 2015 |  | March 31, 2016 |  | December 31, 2015 |  | March 31, 2016 |  | December 31, 2015
Cost of removal obligations |  | $408.1 |  |  |  | $406.0 |  |  |  | $263.1 |  |  |  | $260.4 |  |  |  | $145.0 |  |  |  | $145.6 |
IPL’s tax benefit riders | 141.1 |  |  | 159.2 |  |  | 141.1 |  |  | 159.2 |  |  | — |  |  | — |
Electric transmission cost recovery | 51.4 |  |  | 43.5 |  |  | 25.5 |  |  | 21.9 |  |  | 25.9 |  |  | 21.6 |
Energy efficiency cost recovery | 41.6 |  |  | 48.3 |  |  | — |  |  | — |  |  | 41.6 |  |  | 48.3 |
Commodity cost recovery | 35.2 |  |  | 37.6 |  |  | 20.4 |  |  | 23.5 |  |  | 14.8 |  |  | 14.1 |
Other | 33.6 |  |  | 43.1 |  |  | 18.1 |  |  | 24.2 |  |  | 15.5 |  |  | 18.9 |
|  | $711.0 |  |  |  | $737.7 |  |  |  | $468.2 |  |  |  | $489.2 |  |  |  | $242.8 |  |  |  | $248.5 |
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 for such property-related differences at IPL are recorded to regulatory assets, along with the necessary revenue requirement tax gross-ups. During the three months ended March 31, 2016, Alliant Energy’s and IPL’s tax-related regulatory assets increased primarily due to property-related differences for qualifying repair expenditures. Derivatives - Refer to Note 12 for discussion of derivative assets and derivative liabilities. IPL’s tax benefit riders - IPL’s tax benefit riders utilize regulatory liabilities to credit bills of IPL’s Iowa retail electric and gas customers 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, allocation of insurance proceeds from floods in 2008, and cost of removal expenditures. For the three months ended March 31, 2016, Alliant Energy’s and IPL’s “IPL’s tax benefit riders” regulatory liabilities decreased by $18 million as follows (in millions):
Electric tax benefit rider credits |  | $15 |
Gas tax benefit rider credits | 3 |
|  | $18 |
Refer to Note 8 for additional details regarding IPL’s tax benefit riders. Utility Rate Cases - IPL’s Iowa Retail Electric Rate Settlement Agreement - The IUB approved a settlement agreement in 2014 related to rates charged to IPL’s Iowa retail electric customers. The settlement agreement extends IPL’s Iowa retail electric base rates authorized in its 2009 Test Year rate case through 2016 and provides targeted retail electric customer billing credits. For the three months ended March 31, IPL recorded billing credits to reduce retail electric customers’ bills as follows (in millions):
| 2016 |  | 2015
Billing credits to reduce retail electric customers’ bills | $2 |  |  | $6 |
IPL [Member] |
Public Utilities, General Disclosures [Line Items] |
Regulatory Matters | REGULATORY MATTERS Regulatory Assets and Regulatory Liabilities - Regulatory assets were comprised of the following items (in millions):
| Alliant Energy |  | IPL |  | WPL
| March 31, 2016 |  | December 31, 2015 |  | March 31, 2016 |  | December 31, 2015 |  | March 31, 2016 |  | December 31, 2015
Tax-related |  | $1,002.7 |  |  |  | $987.7 |  |  |  | $972.0 |  |  |  | $958.2 |  |  |  | $30.7 |  |  |  | $29.5 |
Pension and OPEB costs | 570.0 |  |  | 579.5 |  |  | 293.6 |  |  | 298.1 |  |  | 276.4 |  |  | 281.4 |
AROs | 96.1 |  |  | 92.4 |  |  | 54.1 |  |  | 50.8 |  |  | 42.0 |  |  | 41.6 |
Derivatives | 86.6 |  |  | 70.6 |  |  | 25.5 |  |  | 28.2 |  |  | 61.1 |  |  | 42.4 |
WPL’s EGUs retired early | 43.2 |  |  | 45.0 |  |  | — |  |  | — |  |  | 43.2 |  |  | 45.0 |
Emission allowances | 26.7 |  |  | 26.9 |  |  | 26.7 |  |  | 26.9 |  |  | — |  |  | — |
Commodity cost recovery | 26.3 |  |  | 35.9 |  |  | 0.3 |  |  | 2.8 |  |  | 26.0 |  |  | 33.1 |
Other | 65.6 |  |  | 70.6 |  |  | 33.7 |  |  | 37.6 |  |  | 31.9 |  |  | 33.0 |
|  | $1,917.2 |  |  |  | $1,908.6 |  |  |  | $1,405.9 |  |  |  | $1,402.6 |  |  |  | $511.3 |  |  |  | $506.0 |
Regulatory liabilities were comprised of the following items (in millions):
| Alliant Energy |  | IPL |  | WPL
| March 31, 2016 |  | December 31, 2015 |  | March 31, 2016 |  | December 31, 2015 |  | March 31, 2016 |  | December 31, 2015
Cost of removal obligations |  | $408.1 |  |  |  | $406.0 |  |  |  | $263.1 |  |  |  | $260.4 |  |  |  | $145.0 |  |  |  | $145.6 |
IPL’s tax benefit riders | 141.1 |  |  | 159.2 |  |  | 141.1 |  |  | 159.2 |  |  | — |  |  | — |
Electric transmission cost recovery | 51.4 |  |  | 43.5 |  |  | 25.5 |  |  | 21.9 |  |  | 25.9 |  |  | 21.6 |
Energy efficiency cost recovery | 41.6 |  |  | 48.3 |  |  | — |  |  | — |  |  | 41.6 |  |  | 48.3 |
Commodity cost recovery | 35.2 |  |  | 37.6 |  |  | 20.4 |  |  | 23.5 |  |  | 14.8 |  |  | 14.1 |
Other | 33.6 |  |  | 43.1 |  |  | 18.1 |  |  | 24.2 |  |  | 15.5 |  |  | 18.9 |
|  | $711.0 |  |  |  | $737.7 |  |  |  | $468.2 |  |  |  | $489.2 |  |  |  | $242.8 |  |  |  | $248.5 |
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 for such property-related differences at IPL are recorded to regulatory assets, along with the necessary revenue requirement tax gross-ups. During the three months ended March 31, 2016, Alliant Energy’s and IPL’s tax-related regulatory assets increased primarily due to property-related differences for qualifying repair expenditures. Derivatives - Refer to Note 12 for discussion of derivative assets and derivative liabilities. IPL’s tax benefit riders - IPL’s tax benefit riders utilize regulatory liabilities to credit bills of IPL’s Iowa retail electric and gas customers 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, allocation of insurance proceeds from floods in 2008, and cost of removal expenditures. For the three months ended March 31, 2016, Alliant Energy’s and IPL’s “IPL’s tax benefit riders” regulatory liabilities decreased by $18 million as follows (in millions):
Electric tax benefit rider credits |  | $15 |
Gas tax benefit rider credits | 3 |
|  | $18 |
Refer to Note 8 for additional details regarding IPL’s tax benefit riders. Utility Rate Cases - IPL’s Iowa Retail Electric Rate Settlement Agreement - The IUB approved a settlement agreement in 2014 related to rates charged to IPL’s Iowa retail electric customers. The settlement agreement extends IPL’s Iowa retail electric base rates authorized in its 2009 Test Year rate case through 2016 and provides targeted retail electric customer billing credits. For the three months ended March 31, IPL recorded billing credits to reduce retail electric customers’ bills as follows (in millions):
| 2016 |  | 2015
Billing credits to reduce retail electric customers’ bills | $2 |  |  | $6 |
WPL [Member] |
Public Utilities, General Disclosures [Line Items] |
Regulatory Matters | REGULATORY MATTERS Regulatory Assets and Regulatory Liabilities - Regulatory assets were comprised of the following items (in millions):
| Alliant Energy |  | IPL |  | WPL
| March 31, 2016 |  | December 31, 2015 |  | March 31, 2016 |  | December 31, 2015 |  | March 31, 2016 |  | December 31, 2015
Tax-related |  | $1,002.7 |  |  |  | $987.7 |  |  |  | $972.0 |  |  |  | $958.2 |  |  |  | $30.7 |  |  |  | $29.5 |
Pension and OPEB costs | 570.0 |  |  | 579.5 |  |  | 293.6 |  |  | 298.1 |  |  | 276.4 |  |  | 281.4 |
AROs | 96.1 |  |  | 92.4 |  |  | 54.1 |  |  | 50.8 |  |  | 42.0 |  |  | 41.6 |
Derivatives | 86.6 |  |  | 70.6 |  |  | 25.5 |  |  | 28.2 |  |  | 61.1 |  |  | 42.4 |
WPL’s EGUs retired early | 43.2 |  |  | 45.0 |  |  | — |  |  | — |  |  | 43.2 |  |  | 45.0 |
Emission allowances | 26.7 |  |  | 26.9 |  |  | 26.7 |  |  | 26.9 |  |  | — |  |  | — |
Commodity cost recovery | 26.3 |  |  | 35.9 |  |  | 0.3 |  |  | 2.8 |  |  | 26.0 |  |  | 33.1 |
Other | 65.6 |  |  | 70.6 |  |  | 33.7 |  |  | 37.6 |  |  | 31.9 |  |  | 33.0 |
|  | $1,917.2 |  |  |  | $1,908.6 |  |  |  | $1,405.9 |  |  |  | $1,402.6 |  |  |  | $511.3 |  |  |  | $506.0 |
Regulatory liabilities were comprised of the following items (in millions):
| Alliant Energy |  | IPL |  | WPL
| March 31, 2016 |  | December 31, 2015 |  | March 31, 2016 |  | December 31, 2015 |  | March 31, 2016 |  | December 31, 2015
Cost of removal obligations |  | $408.1 |  |  |  | $406.0 |  |  |  | $263.1 |  |  |  | $260.4 |  |  |  | $145.0 |  |  |  | $145.6 |
IPL’s tax benefit riders | 141.1 |  |  | 159.2 |  |  | 141.1 |  |  | 159.2 |  |  | — |  |  | — |
Electric transmission cost recovery | 51.4 |  |  | 43.5 |  |  | 25.5 |  |  | 21.9 |  |  | 25.9 |  |  | 21.6 |
Energy efficiency cost recovery | 41.6 |  |  | 48.3 |  |  | — |  |  | — |  |  | 41.6 |  |  | 48.3 |
Commodity cost recovery | 35.2 |  |  | 37.6 |  |  | 20.4 |  |  | 23.5 |  |  | 14.8 |  |  | 14.1 |
Other | 33.6 |  |  | 43.1 |  |  | 18.1 |  |  | 24.2 |  |  | 15.5 |  |  | 18.9 |
|  | $711.0 |  |  |  | $737.7 |  |  |  | $468.2 |  |  |  | $489.2 |  |  |  | $242.8 |  |  |  | $248.5 |
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 for such property-related differences at IPL are recorded to regulatory assets, along with the necessary revenue requirement tax gross-ups. During the three months ended March 31, 2016, Alliant Energy’s and IPL’s tax-related regulatory assets increased primarily due to property-related differences for qualifying repair expenditures. Derivatives - Refer to Note 12 for discussion of derivative assets and derivative liabilities. IPL’s tax benefit riders - IPL’s tax benefit riders utilize regulatory liabilities to credit bills of IPL’s Iowa retail electric and gas customers 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, allocation of insurance proceeds from floods in 2008, and cost of removal expenditures. For the three months ended March 31, 2016, Alliant Energy’s and IPL’s “IPL’s tax benefit riders” regulatory liabilities decreased by $18 million as follows (in millions):
Electric tax benefit rider credits |  | $15 |
Gas tax benefit rider credits | 3 |
|  | $18 |
Refer to Note 8 for additional details regarding IPL’s tax benefit riders. Utility Rate Cases - IPL’s Iowa Retail Electric Rate Settlement Agreement - The IUB approved a settlement agreement in 2014 related to rates charged to IPL’s Iowa retail electric customers. The settlement agreement extends IPL’s Iowa retail electric base rates authorized in its 2009 Test Year rate case through 2016 and provides targeted retail electric customer billing credits. For the three months ended March 31, IPL recorded billing credits to reduce retail electric customers’ bills as follows (in millions):
| 2016 |  | 2015
Billing credits to reduce retail electric customers’ bills | $2 |  |  | $6 |

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