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Regulatory Matters (Tables) | 12 Months Ended
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Dec. 31, 2013
Regulatory Assets [Line Items] |
Schedule of Regulatory Assets | At December 31, regulatory assets were comprised of the following items (in millions):
| Alliant Energy |  | IPL |  | WPL
| 2013 |  | 2012 |  | 2013 |  | 2012 |  | 2013 |  | 2012
Tax-related |  | $829.7 |  |  |  | $770.7 |  |  |  | $798.6 |  |  |  | $746.2 |  |  |  | $31.1 |  |  |  | $24.5 |
Pension and other postretirement benefits costs | 355.3 |  |  | 549.2 |  |  | 174.2 |  |  | 279.3 |  |  | 181.1 |  |  | 269.9 |
AROs | 65.7 |  |  | 62.4 |  |  | 36.7 |  |  | 38.6 |  |  | 29.0 |  |  | 23.8 |
Emission allowances | 30.0 |  |  | 30.0 |  |  | 30.0 |  |  | 30.0 |  |  | — |  |  | — |
Environmental-related costs | 25.0 |  |  | 34.9 |  |  | 21.0 |  |  | 30.3 |  |  | 4.0 |  |  | 4.6 |
Derivatives | 21.1 |  |  | 40.2 |  |  | 5.9 |  |  | 16.3 |  |  | 15.2 |  |  | 23.9 |
Debt redemption costs | 17.9 |  |  | 19.8 |  |  | 12.2 |  |  | 13.6 |  |  | 5.7 |  |  | 6.2 |
IPL’s electric transmission service costs | 8.3 |  |  | 16.6 |  |  | 8.3 |  |  | 16.6 |  |  | — |  |  | — |
Other | 60.2 |  |  | 88.6 |  |  | 26.6 |  |  | 47.0 |  |  | 33.6 |  |  | 41.6 |
|  | $1,413.2 |  |  |  | $1,612.4 |  |  |  | $1,113.5 |  |  |  | $1,217.9 |  |  |  | $299.7 |  |  |  | $394.5 |
Schedule of Regulatory Liabilities | At December 31, regulatory liabilities were comprised of the following items (in millions):
| Alliant Energy |  | IPL |  | WPL
| 2013 |  | 2012 |  | 2013 |  | 2012 |  | 2013 |  | 2012
Cost of removal obligations |  | $418.9 |  |  |  | $408.7 |  |  |  | $277.7 |  |  |  | $268.0 |  |  |  | $141.2 |  |  |  | $140.7 |
IPL’s tax benefit riders | 265.4 |  |  | 355.8 |  |  | 265.4 |  |  | 355.8 |  |  | — |  |  | — |
Energy conservation cost recovery | 52.7 |  |  | 55.1 |  |  | 9.3 |  |  | 10.0 |  |  | 43.4 |  |  | 45.1 |
IPL’s electric transmission assets sale | 21.6 |  |  | 32.5 |  |  | 21.6 |  |  | 32.5 |  |  | — |  |  | — |
IPL’s electric transmission cost recovery | 14.6 |  |  | — |  |  | 14.6 |  |  | — |  |  | — |  |  | — |
Commodity cost recovery | 7.5 |  |  | 17.7 |  |  | 5.5 |  |  | 5.2 |  |  | 2.0 |  |  | 12.5 |
Other | 40.8 |  |  | 46.3 |  |  | 20.8 |  |  | 29.9 |  |  | 20.0 |  |  | 16.4 |
|  | $821.5 |  |  |  | $916.1 |  |  |  | $614.9 |  |  |  | $701.4 |  |  |  | $206.6 |  |  |  | $214.7 |
IPL [Member] |
Regulatory Assets [Line Items] |
Schedule of Regulatory Assets | At December 31, regulatory assets were comprised of the following items (in millions):
| Alliant Energy |  | IPL |  | WPL
| 2013 |  | 2012 |  | 2013 |  | 2012 |  | 2013 |  | 2012
Tax-related |  | $829.7 |  |  |  | $770.7 |  |  |  | $798.6 |  |  |  | $746.2 |  |  |  | $31.1 |  |  |  | $24.5 |
Pension and other postretirement benefits costs | 355.3 |  |  | 549.2 |  |  | 174.2 |  |  | 279.3 |  |  | 181.1 |  |  | 269.9 |
AROs | 65.7 |  |  | 62.4 |  |  | 36.7 |  |  | 38.6 |  |  | 29.0 |  |  | 23.8 |
Emission allowances | 30.0 |  |  | 30.0 |  |  | 30.0 |  |  | 30.0 |  |  | — |  |  | — |
Environmental-related costs | 25.0 |  |  | 34.9 |  |  | 21.0 |  |  | 30.3 |  |  | 4.0 |  |  | 4.6 |
Derivatives | 21.1 |  |  | 40.2 |  |  | 5.9 |  |  | 16.3 |  |  | 15.2 |  |  | 23.9 |
Debt redemption costs | 17.9 |  |  | 19.8 |  |  | 12.2 |  |  | 13.6 |  |  | 5.7 |  |  | 6.2 |
IPL’s electric transmission service costs | 8.3 |  |  | 16.6 |  |  | 8.3 |  |  | 16.6 |  |  | — |  |  | — |
Other | 60.2 |  |  | 88.6 |  |  | 26.6 |  |  | 47.0 |  |  | 33.6 |  |  | 41.6 |
|  | $1,413.2 |  |  |  | $1,612.4 |  |  |  | $1,113.5 |  |  |  | $1,217.9 |  |  |  | $299.7 |  |  |  | $394.5 |
Schedule of Regulatory Liabilities | At December 31, regulatory liabilities were comprised of the following items (in millions):
| Alliant Energy |  | IPL |  | WPL
| 2013 |  | 2012 |  | 2013 |  | 2012 |  | 2013 |  | 2012
Cost of removal obligations |  | $418.9 |  |  |  | $408.7 |  |  |  | $277.7 |  |  |  | $268.0 |  |  |  | $141.2 |  |  |  | $140.7 |
IPL’s tax benefit riders | 265.4 |  |  | 355.8 |  |  | 265.4 |  |  | 355.8 |  |  | — |  |  | — |
Energy conservation cost recovery | 52.7 |  |  | 55.1 |  |  | 9.3 |  |  | 10.0 |  |  | 43.4 |  |  | 45.1 |
IPL’s electric transmission assets sale | 21.6 |  |  | 32.5 |  |  | 21.6 |  |  | 32.5 |  |  | — |  |  | — |
IPL’s electric transmission cost recovery | 14.6 |  |  | — |  |  | 14.6 |  |  | — |  |  | — |  |  | — |
Commodity cost recovery | 7.5 |  |  | 17.7 |  |  | 5.5 |  |  | 5.2 |  |  | 2.0 |  |  | 12.5 |
Other | 40.8 |  |  | 46.3 |  |  | 20.8 |  |  | 29.9 |  |  | 20.0 |  |  | 16.4 |
|  | $821.5 |  |  |  | $916.1 |  |  |  | $614.9 |  |  |  | $701.4 |  |  |  | $206.6 |  |  |  | $214.7 |
WPL [Member] |
Regulatory Assets [Line Items] |
Schedule of Regulatory Assets | At December 31, regulatory assets were comprised of the following items (in millions):
| Alliant Energy |  | IPL |  | WPL
| 2013 |  | 2012 |  | 2013 |  | 2012 |  | 2013 |  | 2012
Tax-related |  | $829.7 |  |  |  | $770.7 |  |  |  | $798.6 |  |  |  | $746.2 |  |  |  | $31.1 |  |  |  | $24.5 |
Pension and other postretirement benefits costs | 355.3 |  |  | 549.2 |  |  | 174.2 |  |  | 279.3 |  |  | 181.1 |  |  | 269.9 |
AROs | 65.7 |  |  | 62.4 |  |  | 36.7 |  |  | 38.6 |  |  | 29.0 |  |  | 23.8 |
Emission allowances | 30.0 |  |  | 30.0 |  |  | 30.0 |  |  | 30.0 |  |  | — |  |  | — |
Environmental-related costs | 25.0 |  |  | 34.9 |  |  | 21.0 |  |  | 30.3 |  |  | 4.0 |  |  | 4.6 |
Derivatives | 21.1 |  |  | 40.2 |  |  | 5.9 |  |  | 16.3 |  |  | 15.2 |  |  | 23.9 |
Debt redemption costs | 17.9 |  |  | 19.8 |  |  | 12.2 |  |  | 13.6 |  |  | 5.7 |  |  | 6.2 |
IPL’s electric transmission service costs | 8.3 |  |  | 16.6 |  |  | 8.3 |  |  | 16.6 |  |  | — |  |  | — |
Other | 60.2 |  |  | 88.6 |  |  | 26.6 |  |  | 47.0 |  |  | 33.6 |  |  | 41.6 |
|  | $1,413.2 |  |  |  | $1,612.4 |  |  |  | $1,113.5 |  |  |  | $1,217.9 |  |  |  | $299.7 |  |  |  | $394.5 |
Schedule of Regulatory Liabilities | At December 31, regulatory liabilities were comprised of the following items (in millions):
| Alliant Energy |  | IPL |  | WPL
| 2013 |  | 2012 |  | 2013 |  | 2012 |  | 2013 |  | 2012
Cost of removal obligations |  | $418.9 |  |  |  | $408.7 |  |  |  | $277.7 |  |  |  | $268.0 |  |  |  | $141.2 |  |  |  | $140.7 |
IPL’s tax benefit riders | 265.4 |  |  | 355.8 |  |  | 265.4 |  |  | 355.8 |  |  | — |  |  | — |
Energy conservation cost recovery | 52.7 |  |  | 55.1 |  |  | 9.3 |  |  | 10.0 |  |  | 43.4 |  |  | 45.1 |
IPL’s electric transmission assets sale | 21.6 |  |  | 32.5 |  |  | 21.6 |  |  | 32.5 |  |  | — |  |  | — |
IPL’s electric transmission cost recovery | 14.6 |  |  | — |  |  | 14.6 |  |  | — |  |  | — |  |  | — |
Commodity cost recovery | 7.5 |  |  | 17.7 |  |  | 5.5 |  |  | 5.2 |  |  | 2.0 |  |  | 12.5 |
Other | 40.8 |  |  | 46.3 |  |  | 20.8 |  |  | 29.9 |  |  | 20.0 |  |  | 16.4 |
|  | $821.5 |  |  |  | $916.1 |  |  |  | $614.9 |  |  |  | $701.4 |  |  |  | $206.6 |  |  |  | $214.7 |

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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 1 -URI http://asc.fasb.org/extlink&oid=6499975&loc=d3e44250-110382 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 2 -URI http://asc.fasb.org/extlink&oid=6499975&loc=d3e44264-110382 + Details
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