XML 26 R7.htm IDEA: XBRL DOCUMENT
v3.5.0.2

Regulatory Matters | 6 Months Ended
--- | ---
Jun. 30, 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
| June 30, 2016 |  | December 31, 2015 |  | June 30, 2016 |  | December 31, 2015 |  | June 30, 2016 |  | December 31, 2015
Tax-related |  | $1,020.1 |  |  |  | $987.7 |  |  |  | $988.1 |  |  |  | $958.2 |  |  |  | $32.0 |  |  |  | $29.5 |
Pension and OPEB costs | 560.5 |  |  | 579.5 |  |  | 289.2 |  |  | 298.1 |  |  | 271.3 |  |  | 281.4 |
AROs | 99.7 |  |  | 92.4 |  |  | 57.7 |  |  | 50.8 |  |  | 42.0 |  |  | 41.6 |
WPL’s EGUs retired early | 41.5 |  |  | 45.0 |  |  | — |  |  | — |  |  | 41.5 |  |  | 45.0 |
Derivatives | 38.7 |  |  | 70.6 |  |  | 11.0 |  |  | 28.2 |  |  | 27.7 |  |  | 42.4 |
Emission allowances | 26.6 |  |  | 26.9 |  |  | 26.6 |  |  | 26.9 |  |  | — |  |  | — |
Commodity cost recovery | 19.8 |  |  | 35.9 |  |  | 0.3 |  |  | 2.8 |  |  | 19.5 |  |  | 33.1 |
Other | 65.7 |  |  | 70.6 |  |  | 32.5 |  |  | 37.6 |  |  | 33.2 |  |  | 33.0 |
|  | $1,872.6 |  |  |  | $1,908.6 |  |  |  | $1,405.4 |  |  |  | $1,402.6 |  |  |  | $467.2 |  |  |  | $506.0 |
Regulatory liabilities were comprised of the following items (in millions):
| Alliant Energy |  | IPL |  | WPL
| June 30, 2016 |  | December 31, 2015 |  | June 30, 2016 |  | December 31, 2015 |  | June 30, 2016 |  | December 31, 2015
Cost of removal obligations |  | $408.8 |  |  |  | $406.0 |  |  |  | $264.8 |  |  |  | $260.4 |  |  |  | $144.0 |  |  |  | $145.6 |
IPL’s tax benefit riders | 123.1 |  |  | 159.2 |  |  | 123.1 |  |  | 159.2 |  |  | — |  |  | — |
Electric transmission cost recovery | 59.5 |  |  | 43.5 |  |  | 31.7 |  |  | 21.9 |  |  | 27.8 |  |  | 21.6 |
Commodity cost recovery | 41.9 |  |  | 37.6 |  |  | 20.5 |  |  | 23.5 |  |  | 21.4 |  |  | 14.1 |
Energy efficiency cost recovery | 35.2 |  |  | 48.3 |  |  | — |  |  | — |  |  | 35.2 |  |  | 48.3 |
Other | 42.8 |  |  | 43.1 |  |  | 23.3 |  |  | 24.2 |  |  | 19.5 |  |  | 18.9 |
|  | $711.3 |  |  |  | $737.7 |  |  |  | $463.4 |  |  |  | $489.2 |  |  |  | $247.9 |  |  |  | $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 six months ended June 30, 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 six months ended June 30, 2016, Alliant Energy’s and IPL’s “IPL’s tax benefit riders” regulatory liabilities decreased by $36 million as follows (in millions):
Electric tax benefit rider credits |  | $30 |
Gas tax benefit rider credits | 6 |
|  | $36 |
Refer to Note 8 for additional details regarding IPL’s tax benefit riders. Utility Rate Cases - WPL’s Wisconsin Retail Electric and Gas Rate Case (2017/2018 Test Period) - In May 2016, WPL filed a retail base rate filing with the PSCW based on a forward-looking test period that includes 2017 and 2018. WPL’s filing was based on a stipulated agreement reached between PSCW staff, intervener groups and WPL. The filing requested approval for WPL to implement a $13 million, or approximately 1%, increase in annual rates for WPL’s retail electric customers. The net increase for 2017 compared to WPL’s retail electric rate case for the 2015/2016 Test Period reflects a $65 million increase in base rates, partially offset by a $52 million reduction in fuel-related costs, using a preliminary estimate for 2017 fuel-related costs. The filing also requested approval for WPL to implement a $9 million, or approximately 13%, increase in annual base rates for WPL’s retail gas customers. Any rate changes granted from this request are expected to be effective January 1, 2017 and extend through the end of 2018. WPL currently expects a decision from the PSCW regarding this base rate filing in the fourth quarter of 2016. 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 and six months ended June 30, IPL recorded billing credits to reduce retail electric customers’ bills as follows (in millions):
| Three Months |  | Six Months
| 2016 |  | 2015 |  | 2016 |  | 2015
Billing credits to reduce retail electric customers’ bills | $2 |  |  | $6 |  |  |  | $4 |  |  |  | $12 |
WPL’s Retail Fuel-related Rate Filing (2015 Test Year) - Pursuant to a 2014 PSCW order, WPL’s 2015 fuel-related costs were subject to deferral since they were outside an annual bandwidth of plus or minus 2% of the approved annual forecasted fuel-related costs. Retail fuel-related costs incurred by WPL in 2015 were lower than fuel-related costs used to determine rates for such period resulting in an over-collection of fuel-related costs. In July 2016, WPL received a decision from the PSCW authorizing a refund of $10 million, including interest, to WPL’s retail electric customers for these over-collections. WPL currently expects to complete the refund in the fourth quarter of 2016.
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
| June 30, 2016 |  | December 31, 2015 |  | June 30, 2016 |  | December 31, 2015 |  | June 30, 2016 |  | December 31, 2015
Tax-related |  | $1,020.1 |  |  |  | $987.7 |  |  |  | $988.1 |  |  |  | $958.2 |  |  |  | $32.0 |  |  |  | $29.5 |
Pension and OPEB costs | 560.5 |  |  | 579.5 |  |  | 289.2 |  |  | 298.1 |  |  | 271.3 |  |  | 281.4 |
AROs | 99.7 |  |  | 92.4 |  |  | 57.7 |  |  | 50.8 |  |  | 42.0 |  |  | 41.6 |
WPL’s EGUs retired early | 41.5 |  |  | 45.0 |  |  | — |  |  | — |  |  | 41.5 |  |  | 45.0 |
Derivatives | 38.7 |  |  | 70.6 |  |  | 11.0 |  |  | 28.2 |  |  | 27.7 |  |  | 42.4 |
Emission allowances | 26.6 |  |  | 26.9 |  |  | 26.6 |  |  | 26.9 |  |  | — |  |  | — |
Commodity cost recovery | 19.8 |  |  | 35.9 |  |  | 0.3 |  |  | 2.8 |  |  | 19.5 |  |  | 33.1 |
Other | 65.7 |  |  | 70.6 |  |  | 32.5 |  |  | 37.6 |  |  | 33.2 |  |  | 33.0 |
|  | $1,872.6 |  |  |  | $1,908.6 |  |  |  | $1,405.4 |  |  |  | $1,402.6 |  |  |  | $467.2 |  |  |  | $506.0 |
Regulatory liabilities were comprised of the following items (in millions):
| Alliant Energy |  | IPL |  | WPL
| June 30, 2016 |  | December 31, 2015 |  | June 30, 2016 |  | December 31, 2015 |  | June 30, 2016 |  | December 31, 2015
Cost of removal obligations |  | $408.8 |  |  |  | $406.0 |  |  |  | $264.8 |  |  |  | $260.4 |  |  |  | $144.0 |  |  |  | $145.6 |
IPL’s tax benefit riders | 123.1 |  |  | 159.2 |  |  | 123.1 |  |  | 159.2 |  |  | — |  |  | — |
Electric transmission cost recovery | 59.5 |  |  | 43.5 |  |  | 31.7 |  |  | 21.9 |  |  | 27.8 |  |  | 21.6 |
Commodity cost recovery | 41.9 |  |  | 37.6 |  |  | 20.5 |  |  | 23.5 |  |  | 21.4 |  |  | 14.1 |
Energy efficiency cost recovery | 35.2 |  |  | 48.3 |  |  | — |  |  | — |  |  | 35.2 |  |  | 48.3 |
Other | 42.8 |  |  | 43.1 |  |  | 23.3 |  |  | 24.2 |  |  | 19.5 |  |  | 18.9 |
|  | $711.3 |  |  |  | $737.7 |  |  |  | $463.4 |  |  |  | $489.2 |  |  |  | $247.9 |  |  |  | $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 six months ended June 30, 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 six months ended June 30, 2016, Alliant Energy’s and IPL’s “IPL’s tax benefit riders” regulatory liabilities decreased by $36 million as follows (in millions):
Electric tax benefit rider credits |  | $30 |
Gas tax benefit rider credits | 6 |
|  | $36 |
Refer to Note 8 for additional details regarding IPL’s tax benefit riders. Utility Rate Cases - WPL’s Wisconsin Retail Electric and Gas Rate Case (2017/2018 Test Period) - In May 2016, WPL filed a retail base rate filing with the PSCW based on a forward-looking test period that includes 2017 and 2018. WPL’s filing was based on a stipulated agreement reached between PSCW staff, intervener groups and WPL. The filing requested approval for WPL to implement a $13 million, or approximately 1%, increase in annual rates for WPL’s retail electric customers. The net increase for 2017 compared to WPL’s retail electric rate case for the 2015/2016 Test Period reflects a $65 million increase in base rates, partially offset by a $52 million reduction in fuel-related costs, using a preliminary estimate for 2017 fuel-related costs. The filing also requested approval for WPL to implement a $9 million, or approximately 13%, increase in annual base rates for WPL’s retail gas customers. Any rate changes granted from this request are expected to be effective January 1, 2017 and extend through the end of 2018. WPL currently expects a decision from the PSCW regarding this base rate filing in the fourth quarter of 2016. 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 and six months ended June 30, IPL recorded billing credits to reduce retail electric customers’ bills as follows (in millions):
| Three Months |  | Six Months
| 2016 |  | 2015 |  | 2016 |  | 2015
Billing credits to reduce retail electric customers’ bills | $2 |  |  | $6 |  |  |  | $4 |  |  |  | $12 |
WPL’s Retail Fuel-related Rate Filing (2015 Test Year) - Pursuant to a 2014 PSCW order, WPL’s 2015 fuel-related costs were subject to deferral since they were outside an annual bandwidth of plus or minus 2% of the approved annual forecasted fuel-related costs. Retail fuel-related costs incurred by WPL in 2015 were lower than fuel-related costs used to determine rates for such period resulting in an over-collection of fuel-related costs. In July 2016, WPL received a decision from the PSCW authorizing a refund of $10 million, including interest, to WPL’s retail electric customers for these over-collections. WPL currently expects to complete the refund in the fourth quarter of 2016.
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
| June 30, 2016 |  | December 31, 2015 |  | June 30, 2016 |  | December 31, 2015 |  | June 30, 2016 |  | December 31, 2015
Tax-related |  | $1,020.1 |  |  |  | $987.7 |  |  |  | $988.1 |  |  |  | $958.2 |  |  |  | $32.0 |  |  |  | $29.5 |
Pension and OPEB costs | 560.5 |  |  | 579.5 |  |  | 289.2 |  |  | 298.1 |  |  | 271.3 |  |  | 281.4 |
AROs | 99.7 |  |  | 92.4 |  |  | 57.7 |  |  | 50.8 |  |  | 42.0 |  |  | 41.6 |
WPL’s EGUs retired early | 41.5 |  |  | 45.0 |  |  | — |  |  | — |  |  | 41.5 |  |  | 45.0 |
Derivatives | 38.7 |  |  | 70.6 |  |  | 11.0 |  |  | 28.2 |  |  | 27.7 |  |  | 42.4 |
Emission allowances | 26.6 |  |  | 26.9 |  |  | 26.6 |  |  | 26.9 |  |  | — |  |  | — |
Commodity cost recovery | 19.8 |  |  | 35.9 |  |  | 0.3 |  |  | 2.8 |  |  | 19.5 |  |  | 33.1 |
Other | 65.7 |  |  | 70.6 |  |  | 32.5 |  |  | 37.6 |  |  | 33.2 |  |  | 33.0 |
|  | $1,872.6 |  |  |  | $1,908.6 |  |  |  | $1,405.4 |  |  |  | $1,402.6 |  |  |  | $467.2 |  |  |  | $506.0 |
Regulatory liabilities were comprised of the following items (in millions):
| Alliant Energy |  | IPL |  | WPL
| June 30, 2016 |  | December 31, 2015 |  | June 30, 2016 |  | December 31, 2015 |  | June 30, 2016 |  | December 31, 2015
Cost of removal obligations |  | $408.8 |  |  |  | $406.0 |  |  |  | $264.8 |  |  |  | $260.4 |  |  |  | $144.0 |  |  |  | $145.6 |
IPL’s tax benefit riders | 123.1 |  |  | 159.2 |  |  | 123.1 |  |  | 159.2 |  |  | — |  |  | — |
Electric transmission cost recovery | 59.5 |  |  | 43.5 |  |  | 31.7 |  |  | 21.9 |  |  | 27.8 |  |  | 21.6 |
Commodity cost recovery | 41.9 |  |  | 37.6 |  |  | 20.5 |  |  | 23.5 |  |  | 21.4 |  |  | 14.1 |
Energy efficiency cost recovery | 35.2 |  |  | 48.3 |  |  | — |  |  | — |  |  | 35.2 |  |  | 48.3 |
Other | 42.8 |  |  | 43.1 |  |  | 23.3 |  |  | 24.2 |  |  | 19.5 |  |  | 18.9 |
|  | $711.3 |  |  |  | $737.7 |  |  |  | $463.4 |  |  |  | $489.2 |  |  |  | $247.9 |  |  |  | $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 six months ended June 30, 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 six months ended June 30, 2016, Alliant Energy’s and IPL’s “IPL’s tax benefit riders” regulatory liabilities decreased by $36 million as follows (in millions):
Electric tax benefit rider credits |  | $30 |
Gas tax benefit rider credits | 6 |
|  | $36 |
Refer to Note 8 for additional details regarding IPL’s tax benefit riders. Utility Rate Cases - WPL’s Wisconsin Retail Electric and Gas Rate Case (2017/2018 Test Period) - In May 2016, WPL filed a retail base rate filing with the PSCW based on a forward-looking test period that includes 2017 and 2018. WPL’s filing was based on a stipulated agreement reached between PSCW staff, intervener groups and WPL. The filing requested approval for WPL to implement a $13 million, or approximately 1%, increase in annual rates for WPL’s retail electric customers. The net increase for 2017 compared to WPL’s retail electric rate case for the 2015/2016 Test Period reflects a $65 million increase in base rates, partially offset by a $52 million reduction in fuel-related costs, using a preliminary estimate for 2017 fuel-related costs. The filing also requested approval for WPL to implement a $9 million, or approximately 13%, increase in annual base rates for WPL’s retail gas customers. Any rate changes granted from this request are expected to be effective January 1, 2017 and extend through the end of 2018. WPL currently expects a decision from the PSCW regarding this base rate filing in the fourth quarter of 2016. 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 and six months ended June 30, IPL recorded billing credits to reduce retail electric customers’ bills as follows (in millions):
| Three Months |  | Six Months
| 2016 |  | 2015 |  | 2016 |  | 2015
Billing credits to reduce retail electric customers’ bills | $2 |  |  | $6 |  |  |  | $4 |  |  |  | $12 |
WPL’s Retail Fuel-related Rate Filing (2015 Test Year) - Pursuant to a 2014 PSCW order, WPL’s 2015 fuel-related costs were subject to deferral since they were outside an annual bandwidth of plus or minus 2% of the approved annual forecasted fuel-related costs. Retail fuel-related costs incurred by WPL in 2015 were lower than fuel-related costs used to determine rates for such period resulting in an over-collection of fuel-related costs. In July 2016, WPL received a decision from the PSCW authorizing a refund of $10 million, including interest, to WPL’s retail electric customers for these over-collections. WPL currently expects to complete the refund in the fourth quarter of 2016.

X
- Definition The entire disclosure for public utilities. + References No definition available. + Details
Name: | us-gaap_PublicUtilitiesDisclosureTextBlock
Namespace Prefix: | us-gaap_
Data Type: | nonnum:textBlockItemType
Balance Type: | na
Period Type: | duration

X
- Definition Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table. + References No definition available. + Details
Name: | us-gaap_PublicUtilitiesGeneralDisclosuresLineItems
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

X
- Details
Name: | dei_LegalEntityAxis=lnt_IplMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | dei_LegalEntityAxis=lnt_WplMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |