v2.4.0.6

Jointly-Owned Electric Utility Plant | 12 Months Ended
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Dec. 31, 2012
Jointly-Owned Electric Utility Plant | JOINTLY-OWNED ELECTRIC UTILITY PLANT Under joint ownership agreements with other utilities, IPL and WPL have undivided ownership interests in jointly-owned coal-fired electric generating facilities. Each of the respective owners is responsible for the financing of its portion of the construction costs. Kilowatt-hour generation and operating expenses are primarily divided between the joint owners on the same basis as ownership. IPL’s and WPL’s shares of expenses from jointly-owned coal-fired electric generating facilities are included in the corresponding operating expenses (e.g., electric production fuel, other operation and maintenance, etc.) in their Consolidated Statements of Income. Refer to Note 1(b) for further discussion of cost of removal obligations. Information relative to IPL’s and WPL’s ownership interest in these jointly-owned coal-fired electric generating facilities at December 31, 2012 was as follows (dollars in millions):
|  |  |  |  |  |  | Accumulated |  | Construction |  | Cost of Removal
| In-service |  | Ownership |  | Plant in |  | Provision for |  | Work in |  | Obligations Included in
| Dates |  | Interest % |  | Service |  | Depreciation |  | Progress |  | Regulatory Liabilities
IPL |  |  |  |  |  |  |  |  |  |  |
Ottumwa Unit 1 | 1981 |  | 48.0 | % |  |  | $239.2 |  |  |  | $118.8 |  |  |  | $84.0 |  |  |  | $12.0 |
George Neal Unit 4 | 1979 |  | 25.7 | % |  | 97.1 |  |  | 67.8 |  |  | 44.5 |  |  | 11.5 |
George Neal Unit 3 | 1975 |  | 28.0 | % |  | 59.1 |  |  | 39.1 |  |  | 27.2 |  |  | 5.6 |
Louisa Unit 1 | 1983 |  | 4.0 | % |  | 35.0 |  |  | 19.2 |  |  | 0.2 |  |  | 3.0 |
|  |  |  |  | 430.4 |  |  | 244.9 |  |  | 155.9 |  |  | 32.1 |
WPL |  |  |  |  |  |  |  |  |  |  |
Columbia Units 1-2 | 1975-1978 |  | 46.2 | % |  | 247.0 |  |  | 157.9 |  |  | 133.5 |  |  | 10.2 |
Edgewater Unit 4 | 1969 |  | 68.2 | % |  | 91.8 |  |  | 49.2 |  |  | 0.4 |  |  | 2.2 |
|  |  |  |  | 338.8 |  |  | 207.1 |  |  | 133.9 |  |  | 12.4 |
Alliant Energy |  |  |  |  |  | $769.2 |  |  |  | $452.0 |  |  |  | $289.8 |  |  |  | $44.5 |
IPL [Member] |
Jointly-Owned Electric Utility Plant | JOINTLY-OWNED ELECTRIC UTILITY PLANT Under joint ownership agreements with other utilities, IPL and WPL have undivided ownership interests in jointly-owned coal-fired electric generating facilities. Each of the respective owners is responsible for the financing of its portion of the construction costs. Kilowatt-hour generation and operating expenses are primarily divided between the joint owners on the same basis as ownership. IPL’s and WPL’s shares of expenses from jointly-owned coal-fired electric generating facilities are included in the corresponding operating expenses (e.g., electric production fuel, other operation and maintenance, etc.) in their Consolidated Statements of Income. Refer to Note 1(b) for further discussion of cost of removal obligations. Information relative to IPL’s and WPL’s ownership interest in these jointly-owned coal-fired electric generating facilities at December 31, 2012 was as follows (dollars in millions):
|  |  |  |  |  |  | Accumulated |  | Construction |  | Cost of Removal
| In-service |  | Ownership |  | Plant in |  | Provision for |  | Work in |  | Obligations Included in
| Dates |  | Interest % |  | Service |  | Depreciation |  | Progress |  | Regulatory Liabilities
IPL |  |  |  |  |  |  |  |  |  |  |
Ottumwa Unit 1 | 1981 |  | 48.0 | % |  |  | $239.2 |  |  |  | $118.8 |  |  |  | $84.0 |  |  |  | $12.0 |
George Neal Unit 4 | 1979 |  | 25.7 | % |  | 97.1 |  |  | 67.8 |  |  | 44.5 |  |  | 11.5 |
George Neal Unit 3 | 1975 |  | 28.0 | % |  | 59.1 |  |  | 39.1 |  |  | 27.2 |  |  | 5.6 |
Louisa Unit 1 | 1983 |  | 4.0 | % |  | 35.0 |  |  | 19.2 |  |  | 0.2 |  |  | 3.0 |
|  |  |  |  | 430.4 |  |  | 244.9 |  |  | 155.9 |  |  | 32.1 |
WPL |  |  |  |  |  |  |  |  |  |  |
Columbia Units 1-2 | 1975-1978 |  | 46.2 | % |  | 247.0 |  |  | 157.9 |  |  | 133.5 |  |  | 10.2 |
Edgewater Unit 4 | 1969 |  | 68.2 | % |  | 91.8 |  |  | 49.2 |  |  | 0.4 |  |  | 2.2 |
|  |  |  |  | 338.8 |  |  | 207.1 |  |  | 133.9 |  |  | 12.4 |
Alliant Energy |  |  |  |  |  | $769.2 |  |  |  | $452.0 |  |  |  | $289.8 |  |  |  | $44.5 |
WPL [Member] |
Jointly-Owned Electric Utility Plant | JOINTLY-OWNED ELECTRIC UTILITY PLANT Under joint ownership agreements with other utilities, IPL and WPL have undivided ownership interests in jointly-owned coal-fired electric generating facilities. Each of the respective owners is responsible for the financing of its portion of the construction costs. Kilowatt-hour generation and operating expenses are primarily divided between the joint owners on the same basis as ownership. IPL’s and WPL’s shares of expenses from jointly-owned coal-fired electric generating facilities are included in the corresponding operating expenses (e.g., electric production fuel, other operation and maintenance, etc.) in their Consolidated Statements of Income. Refer to Note 1(b) for further discussion of cost of removal obligations. Information relative to IPL’s and WPL’s ownership interest in these jointly-owned coal-fired electric generating facilities at December 31, 2012 was as follows (dollars in millions):
|  |  |  |  |  |  | Accumulated |  | Construction |  | Cost of Removal
| In-service |  | Ownership |  | Plant in |  | Provision for |  | Work in |  | Obligations Included in
| Dates |  | Interest % |  | Service |  | Depreciation |  | Progress |  | Regulatory Liabilities
IPL |  |  |  |  |  |  |  |  |  |  |
Ottumwa Unit 1 | 1981 |  | 48.0 | % |  |  | $239.2 |  |  |  | $118.8 |  |  |  | $84.0 |  |  |  | $12.0 |
George Neal Unit 4 | 1979 |  | 25.7 | % |  | 97.1 |  |  | 67.8 |  |  | 44.5 |  |  | 11.5 |
George Neal Unit 3 | 1975 |  | 28.0 | % |  | 59.1 |  |  | 39.1 |  |  | 27.2 |  |  | 5.6 |
Louisa Unit 1 | 1983 |  | 4.0 | % |  | 35.0 |  |  | 19.2 |  |  | 0.2 |  |  | 3.0 |
|  |  |  |  | 430.4 |  |  | 244.9 |  |  | 155.9 |  |  | 32.1 |
WPL |  |  |  |  |  |  |  |  |  |  |
Columbia Units 1-2 | 1975-1978 |  | 46.2 | % |  | 247.0 |  |  | 157.9 |  |  | 133.5 |  |  | 10.2 |
Edgewater Unit 4 | 1969 |  | 68.2 | % |  | 91.8 |  |  | 49.2 |  |  | 0.4 |  |  | 2.2 |
|  |  |  |  | 338.8 |  |  | 207.1 |  |  | 133.9 |  |  | 12.4 |
Alliant Energy |  |  |  |  |  | $769.2 |  |  |  | $452.0 |  |  |  | $289.8 |  |  |  | $44.5 |

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- Definition Jointly Owned Utility Plants Disclosure [Text Block] + References No definition available. + Details
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Namespace Prefix: | lnt_
Data Type: | nonnum:textBlockItemType
Balance Type: | na
Period Type: | duration