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Benefit Plans (Amounts Recognized On The Consolidated Balance Sheets) (Details) (USD $) In Millions, unless otherwise specified | Dec. 31, 2013 | Dec. 31, 2012
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Amounts recognized on the Consolidated Balance Sheets consist of: |  |  |  |
Pension and other benefit obligations | $ (206.6) |  | $ (364.0) |
Amounts recognized in Regulatory Assets, Regulatory Liabilities and AOCL consist of (a): |  |  |  |
Regulatory liability recognized related to other postretirement benefit plans | 5.1 |  | 2.7 |
Pension Plans, Defined Benefit [Member] |  |  |  |
Amounts recognized on the Consolidated Balance Sheets consist of: |  |  |  |
Non-current assets | 0 |  | 0 |
Other current liabilities | (2.4) |  | (2.4) |
Pension and other benefit obligations | (88.1) |  | (239.5) |
Net amount recognized at December 31 | (90.5) |  | (241.9) |
Amounts recognized in Regulatory Assets, Regulatory Liabilities and AOCL consist of (a): |  |  |  |
Net actuarial loss | 348.6 | [1] | 533.4 | [1]
Prior service credit | (7.4) | [1] | (7.2) | [1]
Net amount recognized at December 31 | 341.2 | [1] | 526.2 | [1]
Other Postretirement Benefits Plans [Member] |  |  |  |
Amounts recognized on the Consolidated Balance Sheets consist of: |  |  |  |
Non-current assets | 14.5 |  | 3.5 |
Other current liabilities | (4.8) |  | (2.8) |
Pension and other benefit obligations | (93.5) |  | (100.8) |
Net amount recognized at December 31 | (83.8) |  | (100.1) |
Amounts recognized in Regulatory Assets, Regulatory Liabilities and AOCL consist of (a): |  |  |  |
Net actuarial loss | 38.1 | [1] | 62.1 | [1]
Prior service credit | (28.6) | [1] | (40.5) | [1]
Net amount recognized at December 31 | 9.5 | [1] | 21.6 | [1]
IPL [Member] |  |  |  |
Amounts recognized on the Consolidated Balance Sheets consist of: |  |  |  |
Pension and other benefit obligations | (48.6) |  | (122.9) |
Amounts recognized in Regulatory Assets, Regulatory Liabilities and AOCL consist of (a): |  |  |  |
Regulatory liability recognized related to other postretirement benefit plans | 1.0 |  | 1.4 |
IPL [Member] | Pension Plans, Defined Benefit [Member] |  |  |  |
Amounts recognized on the Consolidated Balance Sheets consist of: |  |  |  |
Non-current assets | 0 |  | 0 |
Other current liabilities | (0.8) |  | (0.8) |
Pension and other benefit obligations | (27.3) |  | (99.6) |
Net amount recognized at December 31 | (28.1) |  | (100.4) |
Amounts recognized in Regulatory Assets, Regulatory Liabilities and AOCL consist of (a): |  |  |  |
Net actuarial loss | 146.1 | [2] | 231.6 | [2]
Prior service credit | (2.6) | [2] | (2.5) | [2]
Net amount recognized at December 31 | 143.5 | [2] | 229.1 | [2]
IPL [Member] | Other Postretirement Benefits Plans [Member] |  |  |  |
Amounts recognized on the Consolidated Balance Sheets consist of: |  |  |  |
Non-current assets | 8.8 |  | 0 |
Other current liabilities | 0 |  | 0 |
Pension and other benefit obligations | (15.4) |  | (17.2) |
Net amount recognized at December 31 | (6.6) |  | (17.2) |
Amounts recognized in Regulatory Assets, Regulatory Liabilities and AOCL consist of (a): |  |  |  |
Net actuarial loss | 18.2 | [2] | 32.0 | [2]
Prior service credit | (15.0) | [2] | (21.3) | [2]
Net amount recognized at December 31 | 3.2 | [2] | 10.7 | [2]
WPL [Member] |  |  |  |
Amounts recognized on the Consolidated Balance Sheets consist of: |  |  |  |
Pension and other benefit obligations | (88.4) |  | (159.7) |
Amounts recognized in Regulatory Assets, Regulatory Liabilities and AOCL consist of (a): |  |  |  |
Regulatory liability recognized related to other postretirement benefit plans | 1.1 |  | 0.2 |
WPL [Member] | Pension Plans, Defined Benefit [Member] |  |  |  |
Amounts recognized on the Consolidated Balance Sheets consist of: |  |  |  |
Non-current assets | 0 |  | 0 |
Other current liabilities | (0.2) |  | (0.2) |
Pension and other benefit obligations | (21.8) |  | (91.1) |
Net amount recognized at December 31 | (22.0) |  | (91.3) |
Amounts recognized in Regulatory Assets, Regulatory Liabilities and AOCL consist of (a): |  |  |  |
Net actuarial loss | 152.2 | [3] | 233.7 | [3]
Prior service credit | (0.7) | [3] | (0.4) | [3]
Net amount recognized at December 31 | 151.5 | [3] | 233.3 | [3]
WPL [Member] | Other Postretirement Benefits Plans [Member] |  |  |  |
Amounts recognized on the Consolidated Balance Sheets consist of: |  |  |  |
Non-current assets | 5.8 |  | 3.5 |
Other current liabilities | (4.8) |  | (2.8) |
Pension and other benefit obligations | (64.9) |  | (67.5) |
Net amount recognized at December 31 | (63.9) |  | (66.8) |
Amounts recognized in Regulatory Assets, Regulatory Liabilities and AOCL consist of (a): |  |  |  |
Net actuarial loss | 18.3 | [3] | 24.3 | [3]
Prior service credit | (9.5) | [3] | (13.4) | [3]
Net amount recognized at December 31 | $ 8.8 | [3] | $ 10.9 | [3]
[1] | Refer to Note 2 and Alliant Energy’s Consolidated Statements of Common Equity for amounts recognized in “Regulatory assets” and “AOCL,” respectively, on Alliant Energy’s Consolidated Balance Sheets. At December 31, 2013 and 2012, $5.1 million and $2.7 million, respectively, of regulatory liabilities were recognized related to Alliant Energy’s other postretirement benefits plans.
[2] | Refer to Note 2 for amounts recognized in “Regulatory assets” on IPL’s Consolidated Balance Sheets. At December 31, 2013 and 2012, $1.0 million and $1.4 million, respectively, of regulatory liabilities were recognized related to IPL’s other postretirement benefits plans.
[3] | Refer to Note 2 for amounts recognized in “Regulatory assets” on WPL’s Consolidated Balance Sheets. At December 31, 2013 and 2012, $1.1 million and $0.2 million, respectively, of regulatory liabilities were recognized related to WPL’s other postretirement benefits plans.

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