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Regulatory Matters (Tables) | 3 Months Ended
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Mar. 31, 2017
Regulatory Assets [Line Items] |
Regulatory Assets | Regulatory assets were comprised of the following items (in millions):
| Alliant Energy |  | IPL |  | WPL
| March 31, 2017 |  | December 31, 2016 |  | March 31, 2017 |  | December 31, 2016 |  | March 31, 2017 |  | December 31, 2016
Tax-related |  | $1,080.2 |  |  |  | $1,055.6 |  |  |  | $1,044.9 |  |  |  | $1,022.4 |  |  |  | $35.3 |  |  |  | $33.2 |
Pension and OPEB costs | 568.5 |  |  | 578.7 |  |  | 289.1 |  |  | 294.0 |  |  | 279.4 |  |  | 284.7 |
Asset retirement obligations | 108.6 |  |  | 105.9 |  |  | 67.1 |  |  | 64.3 |  |  | 41.5 |  |  | 41.6 |
Derivatives | 46.4 |  |  | 30.7 |  |  | 17.2 |  |  | 10.0 |  |  | 29.2 |  |  | 20.7 |
WPL’s EGUs retired early | 39.7 |  |  | 41.4 |  |  | — |  |  | — |  |  | 39.7 |  |  | 41.4 |
Emission allowances | 26.0 |  |  | 26.2 |  |  | 26.0 |  |  | 26.2 |  |  | — |  |  | — |
Other | 93.6 |  |  | 76.6 |  |  | 56.5 |  |  | 41.9 |  |  | 37.1 |  |  | 34.7 |
|  | $1,963.0 |  |  |  | $1,915.1 |  |  |  | $1,500.8 |  |  |  | $1,458.8 |  |  |  | $462.2 |  |  |  | $456.3 |
Regulatory Liabilities | Regulatory liabilities were comprised of the following items (in millions):
| Alliant Energy |  | IPL |  | WPL
| March 31, 2017 |  | December 31, 2016 |  | March 31, 2017 |  | December 31, 2016 |  | March 31, 2017 |  | December 31, 2016
Cost of removal obligations |  | $413.0 |  |  |  | $411.6 |  |  |  | $271.1 |  |  |  | $269.4 |  |  |  | $141.9 |  |  |  | $142.2 |
Electric transmission cost recovery | 128.3 |  |  | 72.0 |  |  | 75.9 |  |  | 35.7 |  |  | 52.4 |  |  | 36.3 |
IPL’s tax benefit riders | 64.7 |  |  | 83.5 |  |  | 64.7 |  |  | 83.5 |  |  | — |  |  | — |
Commodity cost recovery | 32.9 |  |  | 30.8 |  |  | 20.1 |  |  | 17.8 |  |  | 12.8 |  |  | 13.0 |
Energy efficiency cost recovery | 20.6 |  |  | 20.5 |  |  | — |  |  | — |  |  | 20.6 |  |  | 20.5 |
Derivatives | 9.0 |  |  | 31.5 |  |  | 5.1 |  |  | 12.1 |  |  | 3.9 |  |  | 19.4 |
Other | 28.1 |  |  | 31.1 |  |  | 11.4 |  |  | 12.3 |  |  | 16.7 |  |  | 18.8 |
|  | $696.6 |  |  |  | $681.0 |  |  |  | $448.3 |  |  |  | $430.8 |  |  |  | $248.3 |  |  |  | $250.2 |
Tax Benefit Riders | For the three months ended March 31, 2017, Alliant Energy’s and IPL’s “IPL’s tax benefit riders” regulatory liabilities decreased by $19 million as follows (in millions):
Electric tax benefit rider credits |  | $17 |
Gas tax benefit rider credits | 2 |
|  | $19 |
IPL [Member] |
Regulatory Assets [Line Items] |
Regulatory Assets | Regulatory assets were comprised of the following items (in millions):
| Alliant Energy |  | IPL |  | WPL
| March 31, 2017 |  | December 31, 2016 |  | March 31, 2017 |  | December 31, 2016 |  | March 31, 2017 |  | December 31, 2016
Tax-related |  | $1,080.2 |  |  |  | $1,055.6 |  |  |  | $1,044.9 |  |  |  | $1,022.4 |  |  |  | $35.3 |  |  |  | $33.2 |
Pension and OPEB costs | 568.5 |  |  | 578.7 |  |  | 289.1 |  |  | 294.0 |  |  | 279.4 |  |  | 284.7 |
Asset retirement obligations | 108.6 |  |  | 105.9 |  |  | 67.1 |  |  | 64.3 |  |  | 41.5 |  |  | 41.6 |
Derivatives | 46.4 |  |  | 30.7 |  |  | 17.2 |  |  | 10.0 |  |  | 29.2 |  |  | 20.7 |
WPL’s EGUs retired early | 39.7 |  |  | 41.4 |  |  | — |  |  | — |  |  | 39.7 |  |  | 41.4 |
Emission allowances | 26.0 |  |  | 26.2 |  |  | 26.0 |  |  | 26.2 |  |  | — |  |  | — |
Other | 93.6 |  |  | 76.6 |  |  | 56.5 |  |  | 41.9 |  |  | 37.1 |  |  | 34.7 |
|  | $1,963.0 |  |  |  | $1,915.1 |  |  |  | $1,500.8 |  |  |  | $1,458.8 |  |  |  | $462.2 |  |  |  | $456.3 |
Regulatory Liabilities | Regulatory liabilities were comprised of the following items (in millions):
| Alliant Energy |  | IPL |  | WPL
| March 31, 2017 |  | December 31, 2016 |  | March 31, 2017 |  | December 31, 2016 |  | March 31, 2017 |  | December 31, 2016
Cost of removal obligations |  | $413.0 |  |  |  | $411.6 |  |  |  | $271.1 |  |  |  | $269.4 |  |  |  | $141.9 |  |  |  | $142.2 |
Electric transmission cost recovery | 128.3 |  |  | 72.0 |  |  | 75.9 |  |  | 35.7 |  |  | 52.4 |  |  | 36.3 |
IPL’s tax benefit riders | 64.7 |  |  | 83.5 |  |  | 64.7 |  |  | 83.5 |  |  | — |  |  | — |
Commodity cost recovery | 32.9 |  |  | 30.8 |  |  | 20.1 |  |  | 17.8 |  |  | 12.8 |  |  | 13.0 |
Energy efficiency cost recovery | 20.6 |  |  | 20.5 |  |  | — |  |  | — |  |  | 20.6 |  |  | 20.5 |
Derivatives | 9.0 |  |  | 31.5 |  |  | 5.1 |  |  | 12.1 |  |  | 3.9 |  |  | 19.4 |
Other | 28.1 |  |  | 31.1 |  |  | 11.4 |  |  | 12.3 |  |  | 16.7 |  |  | 18.8 |
|  | $696.6 |  |  |  | $681.0 |  |  |  | $448.3 |  |  |  | $430.8 |  |  |  | $248.3 |  |  |  | $250.2 |
Tax Benefit Riders | For the three months ended March 31, 2017, Alliant Energy’s and IPL’s “IPL’s tax benefit riders” regulatory liabilities decreased by $19 million as follows (in millions):
Electric tax benefit rider credits |  | $17 |
Gas tax benefit rider credits | 2 |
|  | $19 |
WPL [Member] |
Regulatory Assets [Line Items] |
Regulatory Assets | Regulatory assets were comprised of the following items (in millions):
| Alliant Energy |  | IPL |  | WPL
| March 31, 2017 |  | December 31, 2016 |  | March 31, 2017 |  | December 31, 2016 |  | March 31, 2017 |  | December 31, 2016
Tax-related |  | $1,080.2 |  |  |  | $1,055.6 |  |  |  | $1,044.9 |  |  |  | $1,022.4 |  |  |  | $35.3 |  |  |  | $33.2 |
Pension and OPEB costs | 568.5 |  |  | 578.7 |  |  | 289.1 |  |  | 294.0 |  |  | 279.4 |  |  | 284.7 |
Asset retirement obligations | 108.6 |  |  | 105.9 |  |  | 67.1 |  |  | 64.3 |  |  | 41.5 |  |  | 41.6 |
Derivatives | 46.4 |  |  | 30.7 |  |  | 17.2 |  |  | 10.0 |  |  | 29.2 |  |  | 20.7 |
WPL’s EGUs retired early | 39.7 |  |  | 41.4 |  |  | — |  |  | — |  |  | 39.7 |  |  | 41.4 |
Emission allowances | 26.0 |  |  | 26.2 |  |  | 26.0 |  |  | 26.2 |  |  | — |  |  | — |
Other | 93.6 |  |  | 76.6 |  |  | 56.5 |  |  | 41.9 |  |  | 37.1 |  |  | 34.7 |
|  | $1,963.0 |  |  |  | $1,915.1 |  |  |  | $1,500.8 |  |  |  | $1,458.8 |  |  |  | $462.2 |  |  |  | $456.3 |
Regulatory Liabilities | Regulatory liabilities were comprised of the following items (in millions):
| Alliant Energy |  | IPL |  | WPL
| March 31, 2017 |  | December 31, 2016 |  | March 31, 2017 |  | December 31, 2016 |  | March 31, 2017 |  | December 31, 2016
Cost of removal obligations |  | $413.0 |  |  |  | $411.6 |  |  |  | $271.1 |  |  |  | $269.4 |  |  |  | $141.9 |  |  |  | $142.2 |
Electric transmission cost recovery | 128.3 |  |  | 72.0 |  |  | 75.9 |  |  | 35.7 |  |  | 52.4 |  |  | 36.3 |
IPL’s tax benefit riders | 64.7 |  |  | 83.5 |  |  | 64.7 |  |  | 83.5 |  |  | — |  |  | — |
Commodity cost recovery | 32.9 |  |  | 30.8 |  |  | 20.1 |  |  | 17.8 |  |  | 12.8 |  |  | 13.0 |
Energy efficiency cost recovery | 20.6 |  |  | 20.5 |  |  | — |  |  | — |  |  | 20.6 |  |  | 20.5 |
Derivatives | 9.0 |  |  | 31.5 |  |  | 5.1 |  |  | 12.1 |  |  | 3.9 |  |  | 19.4 |
Other | 28.1 |  |  | 31.1 |  |  | 11.4 |  |  | 12.3 |  |  | 16.7 |  |  | 18.8 |
|  | $696.6 |  |  |  | $681.0 |  |  |  | $448.3 |  |  |  | $430.8 |  |  |  | $248.3 |  |  |  | $250.2 |

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- Definition Tabular disclosure of assets that are created when regulatory agencies permit public utilities to defer certain costs included in rate-setting to the balance sheet. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 980 -SubTopic 340 -Section 50 -Paragraph 2 -URI http://asc.fasb.org/extlink&oid=6499975&loc=d3e44264-110382 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 980 -SubTopic 715 -Section 50 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=6501251&loc=d3e52485-110419 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 980 -SubTopic 340 -Section 50 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=6499975&loc=d3e44250-110382 + Details
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- Definition Tabular disclosure of regulatory liabilities. Detailed information about liabilities that result from rate actions of a regulator. Rate actions of a regulator can impose a liability on a regulated enterprise resulting in a regulatory liability. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 980 -SubTopic 405 -Section 25 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=6500807&loc=d3e48068-110394 + Details
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