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Property, Plant and Equipment (Tables) | 12 Months Ended
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Dec. 31, 2018
Property, Plant and Equipment [Line Items] |
Property, Plant and Equipment | At December 31, details of property, plant and equipment on the balance sheets were as follows (in millions):
| Alliant Energy |  | IPL |  | WPL
| 2018 |  | 2017 |  | 2018 |  | 2017 |  | 2018 |  | 2017
Utility: |  |  |  |  |  |  |  |  |  |  |
Electric plant: |  |  |  |  |  |  |  |  |  |  |
Generation in service |  | $6,800.6 |  |  |  | $6,655.3 |  |  |  | $3,610.4 |  |  |  | $3,715.9 |  |  |  | $3,190.2 |  |  |  | $2,939.4 |
Distribution in service | 5,452.2 |  |  | 5,123.5 |  |  | 3,023.7 |  |  | 2,820.9 |  |  | 2,428.5 |  |  | 2,302.6 |
Other in service | 410.8 |  |  | 425.1 |  |  | 260.4 |  |  | 282.3 |  |  | 150.4 |  |  | 142.8 |
Anticipated to be retired early (a) | — |  |  | 93.0 |  |  | — |  |  | — |  |  | — |  |  | 93.0 |
Total electric plant | 12,663.6 |  |  | 12,296.9 |  |  | 6,894.5 |  |  | 6,819.1 |  |  | 5,769.1 |  |  | 5,477.8 |
Gas plant in service | 1,387.6 |  |  | 1,244.0 |  |  | 763.1 |  |  | 654.8 |  |  | 624.5 |  |  | 589.2 |
Other plant in service | 513.2 |  |  | 571.9 |  |  | 322.4 |  |  | 333.4 |  |  | 190.8 |  |  | 238.5 |
Accumulated depreciation | (4,314.6 | ) |  | (4,283.1 | ) |  | (2,294.7 | ) |  | (2,311.0 | ) |  | (2,019.9 | ) |  | (1,972.1 | )
Net plant | 10,249.8 |  |  | 9,829.7 |  |  | 5,685.3 |  |  | 5,496.3 |  |  | 4,564.5 |  |  | 4,333.4 |
Leased Sheboygan Falls Energy Facility, net (b) | — |  |  | — |  |  | — |  |  | — |  |  | 38.1 |  |  | 46.2 |
Construction work in progress | 1,774.8 |  |  | 962.2 |  |  | 1,091.2 |  |  | 424.4 |  |  | 683.6 |  |  | 537.8 |
Other, net | 6.1 |  |  | 6.0 |  |  | 5.0 |  |  | 5.5 |  |  | 1.1 |  |  | 0.5 |
Total utility | 12,030.7 |  |  | 10,797.9 |  |  | 6,781.5 |  |  | 5,926.2 |  |  | 5,287.3 |  |  | 4,917.9 |
Non-utility and other: |  |  |  |  |  |  |  |  |  |  |
Non-utility Generation, net (c) | 86.9 |  |  | 90.9 |  |  | — |  |  | — |  |  | — |  |  | — |
Corporate Services and other, net (d) | 344.8 |  |  | 345.7 |  |  | — |  |  | — |  |  | — |  |  | — |
Total non-utility and other | 431.7 |  |  | 436.6 |  |  | — |  |  | — |  |  | — |  |  | — |
Total property, plant and equipment |  | $12,462.4 |  |  |  | $11,234.5 |  |  |  | $6,781.5 |  |  |  | $5,926.2 |  |  |  | $5,287.3 |  |  |  | $4,917.9 |
(a) | In 2018, WPL retired Edgewater Unit 4 and reclassified the remaining net book value of this EGU from property, plant and equipment to a regulatory asset on Alliant Energy’s and WPL’s balance sheets.
(b) | Less accumulated amortization of $82.8 million and $77.6 million for WPL as of December 31, 2018 and 2017, respectively. The Sheboygan Falls Energy Facility is eliminated from WPL upon consolidation and is included in the “Non-utility Generation, net” line within Alliant Energy’s consolidated property, plant and equipment.
(c) | Less accumulated depreciation of $54.5 million and $50.5 million for Alliant Energy as of December 31, 2018 and 2017, respectively.
(d) | Less accumulated depreciation of $167.5 million and $285.6 million for Alliant Energy as of December 31, 2018 and 2017, respectively.
Allowance For Funds Used During Construction | The amount of AFUDC generated by equity and debt components was as follows (in millions):
| Alliant Energy |  | IPL |  | WPL
| 2018 |  | 2017 |  | 2016 |  | 2018 |  | 2017 |  | 2016 |  | 2018 |  | 2017 |  | 2016
Equity |  | $51.4 |  |  |  | $33.6 |  |  |  | $42.3 |  |  |  | $28.6 |  |  |  | $21.1 |  |  |  | $35.2 |  |  |  | $22.8 |  |  |  | $12.5 |  |  |  | $7.1 |
Debt | 24.2 |  |  | 16.1 |  |  | 20.2 |  |  | 13.6 |  |  | 10.3 |  |  | 16.8 |  |  | 10.6 |  |  | 5.8 |  |  | 3.4 |
|  | $75.6 |  |  |  | $49.7 |  |  |  | $62.5 |  |  |  | $42.2 |  |  |  | $31.4 |  |  |  | $52.0 |  |  |  | $33.4 |  |  |  | $18.3 |  |  |  | $10.5 |
IPL [Member] |
Property, Plant and Equipment [Line Items] |
Property, Plant and Equipment | At December 31, details of property, plant and equipment on the balance sheets were as follows (in millions):
| Alliant Energy |  | IPL |  | WPL
| 2018 |  | 2017 |  | 2018 |  | 2017 |  | 2018 |  | 2017
Utility: |  |  |  |  |  |  |  |  |  |  |
Electric plant: |  |  |  |  |  |  |  |  |  |  |
Generation in service |  | $6,800.6 |  |  |  | $6,655.3 |  |  |  | $3,610.4 |  |  |  | $3,715.9 |  |  |  | $3,190.2 |  |  |  | $2,939.4 |
Distribution in service | 5,452.2 |  |  | 5,123.5 |  |  | 3,023.7 |  |  | 2,820.9 |  |  | 2,428.5 |  |  | 2,302.6 |
Other in service | 410.8 |  |  | 425.1 |  |  | 260.4 |  |  | 282.3 |  |  | 150.4 |  |  | 142.8 |
Anticipated to be retired early (a) | — |  |  | 93.0 |  |  | — |  |  | — |  |  | — |  |  | 93.0 |
Total electric plant | 12,663.6 |  |  | 12,296.9 |  |  | 6,894.5 |  |  | 6,819.1 |  |  | 5,769.1 |  |  | 5,477.8 |
Gas plant in service | 1,387.6 |  |  | 1,244.0 |  |  | 763.1 |  |  | 654.8 |  |  | 624.5 |  |  | 589.2 |
Other plant in service | 513.2 |  |  | 571.9 |  |  | 322.4 |  |  | 333.4 |  |  | 190.8 |  |  | 238.5 |
Accumulated depreciation | (4,314.6 | ) |  | (4,283.1 | ) |  | (2,294.7 | ) |  | (2,311.0 | ) |  | (2,019.9 | ) |  | (1,972.1 | )
Net plant | 10,249.8 |  |  | 9,829.7 |  |  | 5,685.3 |  |  | 5,496.3 |  |  | 4,564.5 |  |  | 4,333.4 |
Leased Sheboygan Falls Energy Facility, net (b) | — |  |  | — |  |  | — |  |  | — |  |  | 38.1 |  |  | 46.2 |
Construction work in progress | 1,774.8 |  |  | 962.2 |  |  | 1,091.2 |  |  | 424.4 |  |  | 683.6 |  |  | 537.8 |
Other, net | 6.1 |  |  | 6.0 |  |  | 5.0 |  |  | 5.5 |  |  | 1.1 |  |  | 0.5 |
Total utility | 12,030.7 |  |  | 10,797.9 |  |  | 6,781.5 |  |  | 5,926.2 |  |  | 5,287.3 |  |  | 4,917.9 |
Non-utility and other: |  |  |  |  |  |  |  |  |  |  |
Non-utility Generation, net (c) | 86.9 |  |  | 90.9 |  |  | — |  |  | — |  |  | — |  |  | — |
Corporate Services and other, net (d) | 344.8 |  |  | 345.7 |  |  | — |  |  | — |  |  | — |  |  | — |
Total non-utility and other | 431.7 |  |  | 436.6 |  |  | — |  |  | — |  |  | — |  |  | — |
Total property, plant and equipment |  | $12,462.4 |  |  |  | $11,234.5 |  |  |  | $6,781.5 |  |  |  | $5,926.2 |  |  |  | $5,287.3 |  |  |  | $4,917.9 |
(a) | In 2018, WPL retired Edgewater Unit 4 and reclassified the remaining net book value of this EGU from property, plant and equipment to a regulatory asset on Alliant Energy’s and WPL’s balance sheets.
(b) | Less accumulated amortization of $82.8 million and $77.6 million for WPL as of December 31, 2018 and 2017, respectively. The Sheboygan Falls Energy Facility is eliminated from WPL upon consolidation and is included in the “Non-utility Generation, net” line within Alliant Energy’s consolidated property, plant and equipment.
(c) | Less accumulated depreciation of $54.5 million and $50.5 million for Alliant Energy as of December 31, 2018 and 2017, respectively.
(d) | Less accumulated depreciation of $167.5 million and $285.6 million for Alliant Energy as of December 31, 2018 and 2017, respectively.
Allowance For Funds Used During Construction | The amount of AFUDC generated by equity and debt components was as follows (in millions):
| Alliant Energy |  | IPL |  | WPL
| 2018 |  | 2017 |  | 2016 |  | 2018 |  | 2017 |  | 2016 |  | 2018 |  | 2017 |  | 2016
Equity |  | $51.4 |  |  |  | $33.6 |  |  |  | $42.3 |  |  |  | $28.6 |  |  |  | $21.1 |  |  |  | $35.2 |  |  |  | $22.8 |  |  |  | $12.5 |  |  |  | $7.1 |
Debt | 24.2 |  |  | 16.1 |  |  | 20.2 |  |  | 13.6 |  |  | 10.3 |  |  | 16.8 |  |  | 10.6 |  |  | 5.8 |  |  | 3.4 |
|  | $75.6 |  |  |  | $49.7 |  |  |  | $62.5 |  |  |  | $42.2 |  |  |  | $31.4 |  |  |  | $52.0 |  |  |  | $33.4 |  |  |  | $18.3 |  |  |  | $10.5 |
WPL [Member] |
Property, Plant and Equipment [Line Items] |
Property, Plant and Equipment | At December 31, details of property, plant and equipment on the balance sheets were as follows (in millions):
| Alliant Energy |  | IPL |  | WPL
| 2018 |  | 2017 |  | 2018 |  | 2017 |  | 2018 |  | 2017
Utility: |  |  |  |  |  |  |  |  |  |  |
Electric plant: |  |  |  |  |  |  |  |  |  |  |
Generation in service |  | $6,800.6 |  |  |  | $6,655.3 |  |  |  | $3,610.4 |  |  |  | $3,715.9 |  |  |  | $3,190.2 |  |  |  | $2,939.4 |
Distribution in service | 5,452.2 |  |  | 5,123.5 |  |  | 3,023.7 |  |  | 2,820.9 |  |  | 2,428.5 |  |  | 2,302.6 |
Other in service | 410.8 |  |  | 425.1 |  |  | 260.4 |  |  | 282.3 |  |  | 150.4 |  |  | 142.8 |
Anticipated to be retired early (a) | — |  |  | 93.0 |  |  | — |  |  | — |  |  | — |  |  | 93.0 |
Total electric plant | 12,663.6 |  |  | 12,296.9 |  |  | 6,894.5 |  |  | 6,819.1 |  |  | 5,769.1 |  |  | 5,477.8 |
Gas plant in service | 1,387.6 |  |  | 1,244.0 |  |  | 763.1 |  |  | 654.8 |  |  | 624.5 |  |  | 589.2 |
Other plant in service | 513.2 |  |  | 571.9 |  |  | 322.4 |  |  | 333.4 |  |  | 190.8 |  |  | 238.5 |
Accumulated depreciation | (4,314.6 | ) |  | (4,283.1 | ) |  | (2,294.7 | ) |  | (2,311.0 | ) |  | (2,019.9 | ) |  | (1,972.1 | )
Net plant | 10,249.8 |  |  | 9,829.7 |  |  | 5,685.3 |  |  | 5,496.3 |  |  | 4,564.5 |  |  | 4,333.4 |
Leased Sheboygan Falls Energy Facility, net (b) | — |  |  | — |  |  | — |  |  | — |  |  | 38.1 |  |  | 46.2 |
Construction work in progress | 1,774.8 |  |  | 962.2 |  |  | 1,091.2 |  |  | 424.4 |  |  | 683.6 |  |  | 537.8 |
Other, net | 6.1 |  |  | 6.0 |  |  | 5.0 |  |  | 5.5 |  |  | 1.1 |  |  | 0.5 |
Total utility | 12,030.7 |  |  | 10,797.9 |  |  | 6,781.5 |  |  | 5,926.2 |  |  | 5,287.3 |  |  | 4,917.9 |
Non-utility and other: |  |  |  |  |  |  |  |  |  |  |
Non-utility Generation, net (c) | 86.9 |  |  | 90.9 |  |  | — |  |  | — |  |  | — |  |  | — |
Corporate Services and other, net (d) | 344.8 |  |  | 345.7 |  |  | — |  |  | — |  |  | — |  |  | — |
Total non-utility and other | 431.7 |  |  | 436.6 |  |  | — |  |  | — |  |  | — |  |  | — |
Total property, plant and equipment |  | $12,462.4 |  |  |  | $11,234.5 |  |  |  | $6,781.5 |  |  |  | $5,926.2 |  |  |  | $5,287.3 |  |  |  | $4,917.9 |
(a) | In 2018, WPL retired Edgewater Unit 4 and reclassified the remaining net book value of this EGU from property, plant and equipment to a regulatory asset on Alliant Energy’s and WPL’s balance sheets.
(b) | Less accumulated amortization of $82.8 million and $77.6 million for WPL as of December 31, 2018 and 2017, respectively. The Sheboygan Falls Energy Facility is eliminated from WPL upon consolidation and is included in the “Non-utility Generation, net” line within Alliant Energy’s consolidated property, plant and equipment.
(c) | Less accumulated depreciation of $54.5 million and $50.5 million for Alliant Energy as of December 31, 2018 and 2017, respectively.
(d) | Less accumulated depreciation of $167.5 million and $285.6 million for Alliant Energy as of December 31, 2018 and 2017, respectively.
Allowance For Funds Used During Construction | The amount of AFUDC generated by equity and debt components was as follows (in millions):
| Alliant Energy |  | IPL |  | WPL
| 2018 |  | 2017 |  | 2016 |  | 2018 |  | 2017 |  | 2016 |  | 2018 |  | 2017 |  | 2016
Equity |  | $51.4 |  |  |  | $33.6 |  |  |  | $42.3 |  |  |  | $28.6 |  |  |  | $21.1 |  |  |  | $35.2 |  |  |  | $22.8 |  |  |  | $12.5 |  |  |  | $7.1 |
Debt | 24.2 |  |  | 16.1 |  |  | 20.2 |  |  | 13.6 |  |  | 10.3 |  |  | 16.8 |  |  | 10.6 |  |  | 5.8 |  |  | 3.4 |
|  | $75.6 |  |  |  | $49.7 |  |  |  | $62.5 |  |  |  | $42.2 |  |  |  | $31.4 |  |  |  | $52.0 |  |  |  | $33.4 |  |  |  | $18.3 |  |  |  | $10.5 |
Forward Wind Energy Center [Member] |
Property, Plant and Equipment [Line Items] |
Assets Purchased and Liabilities Assumed | As of the closing date, the estimated fair value of the assets purchased and the liabilities assumed by WPL were as follows (in millions):
Property, plant and equipment, net |  | $81 |
Liabilities | 7 |
Net assets acquired |  | $74 |
Forward Wind Energy Center [Member] | WPL [Member] |
Property, Plant and Equipment [Line Items] |
Assets Purchased and Liabilities Assumed | As of the closing date, the estimated fair value of the assets purchased and the liabilities assumed by WPL were as follows (in millions):
Property, plant and equipment, net |  | $81 |
Liabilities | 7 |
Net assets acquired |  | $74 |
Franklin County Wind Farm [Member] |
Property, Plant and Equipment [Line Items] |
Assets Purchased and Liabilities Assumed | As of the closing date, the estimated fair values of the assets purchased and liabilities assumed by IPL were as follows (in millions):
Electric plant in service |  | $40 |
Current assets | 2 |
Total assets acquired | 42 |
Other liabilities | 10 |
Net assets acquired |  | $32 |
Franklin County Wind Farm [Member] | IPL [Member] |
Property, Plant and Equipment [Line Items] |
Assets Purchased and Liabilities Assumed | As of the closing date, the estimated fair values of the assets purchased and liabilities assumed by IPL were as follows (in millions):
Electric plant in service |  | $40 |
Current assets | 2 |
Total assets acquired | 42 |
Other liabilities | 10 |
Net assets acquired |  | $32 |

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