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Regulatory Matters (Tables) | 9 Months Ended
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Sep. 30, 2017
Regulatory Assets [Line Items] |
Regulatory Assets | Regulatory assets were comprised of the following items (in millions):
| Alliant Energy |  | IPL |  | WPL
| September 30, 2017 |  | December 31, 2016 |  | September 30, 2017 |  | December 31, 2016 |  | September 30, 2017 |  | December 31, 2016
Tax-related |  | $1,147.9 |  |  |  | $1,055.6 |  |  |  | $1,107.9 |  |  |  | $1,022.4 |  |  |  | $40.0 |  |  |  | $33.2 |
Pension and OPEB costs | 547.8 |  |  | 578.7 |  |  | 279.3 |  |  | 294.0 |  |  | 268.5 |  |  | 284.7 |
Asset retirement obligations | 107.9 |  |  | 105.9 |  |  | 71.9 |  |  | 64.3 |  |  | 36.0 |  |  | 41.6 |
EGUs retired early | 67.4 |  |  | 41.4 |  |  | 32.9 |  |  | — |  |  | 34.5 |  |  | 41.4 |
Derivatives | 49.9 |  |  | 30.7 |  |  | 22.3 |  |  | 10.0 |  |  | 27.6 |  |  | 20.7 |
Emission allowances | 25.6 |  |  | 26.2 |  |  | 25.6 |  |  | 26.2 |  |  | — |  |  | — |
Other | 90.0 |  |  | 76.6 |  |  | 51.0 |  |  | 41.9 |  |  | 39.0 |  |  | 34.7 |
|  | $2,036.5 |  |  |  | $1,915.1 |  |  |  | $1,590.9 |  |  |  | $1,458.8 |  |  |  | $445.6 |  |  |  | $456.3 |
Regulatory Liabilities | Regulatory liabilities were comprised of the following items (in millions):
| Alliant Energy |  | IPL |  | WPL
| September 30, 2017 |  | December 31, 2016 |  | September 30, 2017 |  | December 31, 2016 |  | September 30, 2017 |  | December 31, 2016
Cost of removal obligations |  | $412.1 |  |  |  | $411.6 |  |  |  | $272.9 |  |  |  | $269.4 |  |  |  | $139.2 |  |  |  | $142.2 |
Electric transmission cost recovery | 94.8 |  |  | 72.0 |  |  | 35.9 |  |  | 35.7 |  |  | 58.9 |  |  | 36.3 |
IPL’s tax benefit riders | 45.0 |  |  | 83.5 |  |  | 45.0 |  |  | 83.5 |  |  | — |  |  | — |
Commodity cost recovery | 21.2 |  |  | 30.8 |  |  | 15.0 |  |  | 17.8 |  |  | 6.2 |  |  | 13.0 |
Energy efficiency cost recovery | 20.0 |  |  | 20.5 |  |  | — |  |  | — |  |  | 20.0 |  |  | 20.5 |
Derivatives | 10.9 |  |  | 31.5 |  |  | 5.8 |  |  | 12.1 |  |  | 5.1 |  |  | 19.4 |
Other | 24.5 |  |  | 31.1 |  |  | 10.2 |  |  | 12.3 |  |  | 14.3 |  |  | 18.8 |
|  | $628.5 |  |  |  | $681.0 |  |  |  | $384.8 |  |  |  | $430.8 |  |  |  | $243.7 |  |  |  | $250.2 |
Tax Benefit Riders | For the nine months ended September 30, 2017, Alliant Energy’s and IPL’s “IPL’s tax benefit riders” regulatory liabilities decreased by ($39) million as follows (in millions):
Electric tax benefit rider credits |  | ($51 | )
Gas tax benefit rider credits | (5 | )
Rate-making accounting change | 17 |
|  | ($39 | )
IPL [Member] |
Regulatory Assets [Line Items] |
Regulatory Assets | Regulatory assets were comprised of the following items (in millions):
| Alliant Energy |  | IPL |  | WPL
| September 30, 2017 |  | December 31, 2016 |  | September 30, 2017 |  | December 31, 2016 |  | September 30, 2017 |  | December 31, 2016
Tax-related |  | $1,147.9 |  |  |  | $1,055.6 |  |  |  | $1,107.9 |  |  |  | $1,022.4 |  |  |  | $40.0 |  |  |  | $33.2 |
Pension and OPEB costs | 547.8 |  |  | 578.7 |  |  | 279.3 |  |  | 294.0 |  |  | 268.5 |  |  | 284.7 |
Asset retirement obligations | 107.9 |  |  | 105.9 |  |  | 71.9 |  |  | 64.3 |  |  | 36.0 |  |  | 41.6 |
EGUs retired early | 67.4 |  |  | 41.4 |  |  | 32.9 |  |  | — |  |  | 34.5 |  |  | 41.4 |
Derivatives | 49.9 |  |  | 30.7 |  |  | 22.3 |  |  | 10.0 |  |  | 27.6 |  |  | 20.7 |
Emission allowances | 25.6 |  |  | 26.2 |  |  | 25.6 |  |  | 26.2 |  |  | — |  |  | — |
Other | 90.0 |  |  | 76.6 |  |  | 51.0 |  |  | 41.9 |  |  | 39.0 |  |  | 34.7 |
|  | $2,036.5 |  |  |  | $1,915.1 |  |  |  | $1,590.9 |  |  |  | $1,458.8 |  |  |  | $445.6 |  |  |  | $456.3 |
Regulatory Liabilities | Regulatory liabilities were comprised of the following items (in millions):
| Alliant Energy |  | IPL |  | WPL
| September 30, 2017 |  | December 31, 2016 |  | September 30, 2017 |  | December 31, 2016 |  | September 30, 2017 |  | December 31, 2016
Cost of removal obligations |  | $412.1 |  |  |  | $411.6 |  |  |  | $272.9 |  |  |  | $269.4 |  |  |  | $139.2 |  |  |  | $142.2 |
Electric transmission cost recovery | 94.8 |  |  | 72.0 |  |  | 35.9 |  |  | 35.7 |  |  | 58.9 |  |  | 36.3 |
IPL’s tax benefit riders | 45.0 |  |  | 83.5 |  |  | 45.0 |  |  | 83.5 |  |  | — |  |  | — |
Commodity cost recovery | 21.2 |  |  | 30.8 |  |  | 15.0 |  |  | 17.8 |  |  | 6.2 |  |  | 13.0 |
Energy efficiency cost recovery | 20.0 |  |  | 20.5 |  |  | — |  |  | — |  |  | 20.0 |  |  | 20.5 |
Derivatives | 10.9 |  |  | 31.5 |  |  | 5.8 |  |  | 12.1 |  |  | 5.1 |  |  | 19.4 |
Other | 24.5 |  |  | 31.1 |  |  | 10.2 |  |  | 12.3 |  |  | 14.3 |  |  | 18.8 |
|  | $628.5 |  |  |  | $681.0 |  |  |  | $384.8 |  |  |  | $430.8 |  |  |  | $243.7 |  |  |  | $250.2 |
Tax Benefit Riders | For the nine months ended September 30, 2017, Alliant Energy’s and IPL’s “IPL’s tax benefit riders” regulatory liabilities decreased by ($39) million as follows (in millions):
Electric tax benefit rider credits |  | ($51 | )
Gas tax benefit rider credits | (5 | )
Rate-making accounting change | 17 |
|  | ($39 | )
WPL [Member] |
Regulatory Assets [Line Items] |
Regulatory Assets | Regulatory assets were comprised of the following items (in millions):
| Alliant Energy |  | IPL |  | WPL
| September 30, 2017 |  | December 31, 2016 |  | September 30, 2017 |  | December 31, 2016 |  | September 30, 2017 |  | December 31, 2016
Tax-related |  | $1,147.9 |  |  |  | $1,055.6 |  |  |  | $1,107.9 |  |  |  | $1,022.4 |  |  |  | $40.0 |  |  |  | $33.2 |
Pension and OPEB costs | 547.8 |  |  | 578.7 |  |  | 279.3 |  |  | 294.0 |  |  | 268.5 |  |  | 284.7 |
Asset retirement obligations | 107.9 |  |  | 105.9 |  |  | 71.9 |  |  | 64.3 |  |  | 36.0 |  |  | 41.6 |
EGUs retired early | 67.4 |  |  | 41.4 |  |  | 32.9 |  |  | — |  |  | 34.5 |  |  | 41.4 |
Derivatives | 49.9 |  |  | 30.7 |  |  | 22.3 |  |  | 10.0 |  |  | 27.6 |  |  | 20.7 |
Emission allowances | 25.6 |  |  | 26.2 |  |  | 25.6 |  |  | 26.2 |  |  | — |  |  | — |
Other | 90.0 |  |  | 76.6 |  |  | 51.0 |  |  | 41.9 |  |  | 39.0 |  |  | 34.7 |
|  | $2,036.5 |  |  |  | $1,915.1 |  |  |  | $1,590.9 |  |  |  | $1,458.8 |  |  |  | $445.6 |  |  |  | $456.3 |
Regulatory Liabilities | Regulatory liabilities were comprised of the following items (in millions):
| Alliant Energy |  | IPL |  | WPL
| September 30, 2017 |  | December 31, 2016 |  | September 30, 2017 |  | December 31, 2016 |  | September 30, 2017 |  | December 31, 2016
Cost of removal obligations |  | $412.1 |  |  |  | $411.6 |  |  |  | $272.9 |  |  |  | $269.4 |  |  |  | $139.2 |  |  |  | $142.2 |
Electric transmission cost recovery | 94.8 |  |  | 72.0 |  |  | 35.9 |  |  | 35.7 |  |  | 58.9 |  |  | 36.3 |
IPL’s tax benefit riders | 45.0 |  |  | 83.5 |  |  | 45.0 |  |  | 83.5 |  |  | — |  |  | — |
Commodity cost recovery | 21.2 |  |  | 30.8 |  |  | 15.0 |  |  | 17.8 |  |  | 6.2 |  |  | 13.0 |
Energy efficiency cost recovery | 20.0 |  |  | 20.5 |  |  | — |  |  | — |  |  | 20.0 |  |  | 20.5 |
Derivatives | 10.9 |  |  | 31.5 |  |  | 5.8 |  |  | 12.1 |  |  | 5.1 |  |  | 19.4 |
Other | 24.5 |  |  | 31.1 |  |  | 10.2 |  |  | 12.3 |  |  | 14.3 |  |  | 18.8 |
|  | $628.5 |  |  |  | $681.0 |  |  |  | $384.8 |  |  |  | $430.8 |  |  |  | $243.7 |  |  |  | $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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