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Commitments And Contingencies (Narrative) (Details) (USD $) In Millions, unless otherwise specified | 12 Months Ended |  | 12 Months Ended |  | 12 Months Ended |  | 12 Months Ended | 1 Months Ended |  | 12 Months Ended |  | 12 Months Ended |  | 12 Months Ended | 3 Months Ended | 12 Months Ended | 1 Months Ended |  | 12 Months Ended
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Dec. 31, 2013 | Dec. 31, 2012 | Dec. 31, 2011 | Dec. 31, 2013 Workforce Subject to Collective Bargaining Arrangements [Member] | Dec. 31, 2013 Workforce Subject to Collective Bargaining Arrangements Expiring within One Year [Member] | Dec. 31, 2013 Defined Benefit Pension Plans [Member] | Dec. 31, 2012 Defined Benefit Pension Plans [Member] | Dec. 31, 2011 Defined Benefit Pension Plans [Member] | Dec. 31, 2013 Minimum [Member] | Dec. 31, 2013 Maximum [Member] | Dec. 31, 2013 Manufactured Gas Plant Sites [Member] | Dec. 31, 2013 Scenario, Forecast [Member] | Dec. 31, 2013 Scenario, Forecast [Member] Performance guarantees outstanding, 2014 [Member] | Dec. 31, 2013 Scenario, Forecast [Member] Performance guarantees outstanding, 2015 [Member] | Dec. 31, 2013 Scenario, Forecast [Member] Capital Purchase Obligation [Member] | Dec. 31, 2013 Scenario, Forecast [Member] DAEC IPL [Member] | Dec. 31, 2013 IPL [Member] site | Dec. 31, 2012 IPL [Member] | Dec. 31, 2013 IPL [Member] Workforce Subject to Collective Bargaining Arrangements [Member] | Dec. 31, 2013 IPL [Member] Defined Benefit Pension Plans [Member] | Dec. 31, 2012 IPL [Member] Defined Benefit Pension Plans [Member] | Dec. 31, 2011 IPL [Member] Defined Benefit Pension Plans [Member] | Jan. 31, 2013 IPL [Member] DAEC IPL [Member] MW | Dec. 31, 2013 IPL [Member] Manufactured Gas Plant Sites [Member] | Dec. 31, 2013 IPL [Member] Scenario, Forecast [Member] | Dec. 31, 2013 IPL [Member] Scenario, Forecast [Member] Capital Purchase Obligation [Member] | Dec. 31, 2013 WPL [Member] site | Dec. 31, 2012 WPL [Member] | Dec. 31, 2013 WPL [Member] Workforce Subject to Collective Bargaining Arrangements [Member] | Dec. 31, 2013 WPL [Member] Workforce Subject to Collective Bargaining Arrangements Expiring within One Year [Member] | Dec. 31, 2013 WPL [Member] Defined Benefit Pension Plans [Member] | Dec. 31, 2012 WPL [Member] Defined Benefit Pension Plans [Member] | Dec. 31, 2011 WPL [Member] Defined Benefit Pension Plans [Member] | Dec. 31, 2013 WPL [Member] Manufactured Gas Plant Sites [Member] | Dec. 31, 2013 WPL [Member] Scenario, Forecast [Member] | Dec. 31, 2013 WPL [Member] Scenario, Forecast [Member] Capital Purchase Obligation [Member] | Mar. 31, 2013 Cash Balance Plan [Member] Defined Benefit Pension Plans [Member] | Dec. 31, 2011 Cash Balance Plan [Member] Defined Benefit Pension Plans [Member] | Jan. 31, 2014 Cash Balance Plan [Member] Defined Benefit Pension Plans [Member] Subsequent Event [Member] | Dec. 31, 2013 RMT [Member] Indemnification Agreement [Member] | Dec. 31, 2013 Environmental Issue [Member] WPL [Member] | Dec. 31, 2013 Civil Penalty [Member] WPL [Member]
Long-term Purchase Commitment [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Minimum future commitments |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 2,583 |  |  | $ 86 | $ 1,657 | [1],[2] |  |  |  |  |  |  |  |  |  |  |  | $ 2,028 | $ 35 |  |  |  |  |  |  |  |  |  |  |  | $ 552 | $ 51 |  |  |  |  |  |
Aggregate additional payments to certain plan participants |  |  |  |  |  | 9.0 | [3],[4] | 0.1 | [3],[4] | 10.2 | [3],[4] |  |  |  |  |  |  |  |  |  |  |  |  | 2.6 | [3],[4] | 0 | [3],[4] | 2.8 | [3],[4] |  |  |  |  |  |  |  |  | 0.6 | [3],[4] | 0.1 | [3],[4] | 0.7 | [3],[4] |  |  |  |  | 10.0 |  |  |  |
Final judgment from court order |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 9.0 |  |  |
Plaintiffs' attorney's fees and costs |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 6.7 |  |  |  |  |
Loss contingency, estimated amount |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 3 |  |
Warranty period |  |  |  |  |  |  |  |  |  |  |  | 12 months | 60 months |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Performance guarantees outstanding |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 347 | 294 | 53 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Present value abandonment obligation |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 32 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Number of sites monitoring and/or remediating (in sites) |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 27 |  |  |  |  |  |  |  |  |  |  |  |  | 5 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Minimum remaining estimated cost incurred for investigation, remediation and monitoring |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 13 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 11 |  |  |  |  |  |  |  |  |  |  |  |  | 2 |  |  |  |  |  |  |
Maximum remaining estimated cost incurred for investigation, remediation and monitoring |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 30 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 27 |  |  |  |  |  |  |  |  |  |  |  |  | 3 |  |  |  |  |  |  |
Current and non-current environmental liabilities | 19.0 | 29.0 |  |  |  |  |  |  |  |  |  |  |  | 19.0 |  |  |  |  |  |  | 16.4 | 25.7 |  |  |  |  |  |  |  |  | 16.0 |  |  | 2.5 | 3.3 |  |  |  |  |  |  |  |  | 3.0 |  |  |  |  |  |  |  |
Damages awarded |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 7 | $ 2
Approved amount of electric power capacity (in megawatts) |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 431 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Concentration risk | 100.00% | 100.00% | 100.00% | 57.00% | 26.00% |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 67.00% |  |  |  |  |  |  |  |  |  |  |  |  | 80.00% | 80.00% |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
[1] | Includes commitments incurred under an existing PPA that expires February 2014 and a new PPA effective February 2014. The new PPA grants IPL rights to purchase 431 MWs of capacity and the resulting energy from DAEC for a term from the expiration of the existing PPA in February 2014 through December 31, 2025. If energy delivered under the new PPA is less than the targeted energy amount, an adjustment payment will be made to IPL, which will be reflected in IPL’s fuel adjustment clause.
[2] | Includes payments required by PPAs for capacity rights (Alliant Energy and IPL only) and minimum quantities of MWhs required to be purchased. Refer to Note 18 for additional information on purchased power transactions.
[3] | Alliant Energy reached an agreement with the IRS, which resulted in a favorable determination letter for the Cash Balance Plan in 2011. The agreement with the IRS required Alliant Energy to amend the Cash Balance Plan, which was completed in 2011 resulting in aggregate additional benefits of $10.2 million paid by Alliant Energy to certain former participants in the Cash Balance Plan in 2011. Alliant Energy recognized $10.2 million of additional benefits costs in 2011 related to these benefits. IPL recognized $6.3 million ($2.8 million directly assigned and $3.5 million allocated by Corporate Services) and WPL recognized $3.4 million ($0.7 million directly assigned and $2.7 million allocated by Corporate Services) of additional benefits costs in 2011 related to these benefits. Refer to Note 16(c) for additional information regarding the Cash Balance Plan.
[4] | In 2013, Alliant Energy filed a stipulation agreement with the Court related to the class-action lawsuit against the Cash Balance Plan. As a result, Alliant Energy recognized $9.0 million of additional benefits costs in 2013 related to the agreement. IPL recognized $5.5 million ($2.6 million directly assigned and $2.9 million allocated by Corporate Services) and WPL recognized $2.8 million ($0.6 million directly assigned and $2.2 million allocated by Corporate Services) of additional benefits costs in 2013 related to the agreement. Refer to Note 16(c) for additional information regarding the Cash Balance Plan.

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