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Regulatory Matters (Tables) | 6 Months Ended
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Jun. 30, 2016
Regulatory Assets [Line Items] |
Regulatory Assets | 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 | 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 Benefit Riders | 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 |
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 |
IPL [Member] |
Regulatory Assets [Line Items] |
Regulatory Assets | 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 | 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 Benefit Riders | 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 |
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 [Member] |
Regulatory Assets [Line Items] |
Regulatory Assets | 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 | 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 |

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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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