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Commitments And Contingencies (Operating Expense Purchase Obligations) (Details) (USD $) In Millions, unless otherwise specified | 3 Months Ended
--- | ---
Mar. 31, 2014
Long-term Purchase Commitment [Line Items] |  |
Individual commitments incurred | $ 1 |
Scenario, Forecast [Member] |  |
Long-term Purchase Commitment [Line Items] |  |
Minimum future commitments | 2,518 |
Scenario, Forecast [Member] | IPL [Member] |  |
Long-term Purchase Commitment [Line Items] |  |
Minimum future commitments | 1,955 |
Scenario, Forecast [Member] | WPL [Member] |  |
Long-term Purchase Commitment [Line Items] |  |
Minimum future commitments | 560 |
Scenario, Forecast [Member] | Other [Member] |  |
Long-term Purchase Commitment [Line Items] |  |
Minimum future commitments | 33 | [1]
Scenario, Forecast [Member] | Other [Member] | IPL [Member] |  |
Long-term Purchase Commitment [Line Items] |  |
Minimum future commitments | 21 | [1]
Scenario, Forecast [Member] | Other [Member] | WPL [Member] |  |
Long-term Purchase Commitment [Line Items] |  |
Minimum future commitments | 9 | [1]
Scenario, Forecast [Member] | Natural Gas [Member] |  |
Long-term Purchase Commitment [Line Items] |  |
Minimum future commitments | 276 |
Scenario, Forecast [Member] | Natural Gas [Member] | IPL [Member] |  |
Long-term Purchase Commitment [Line Items] |  |
Minimum future commitments | 146 |
Scenario, Forecast [Member] | Natural Gas [Member] | WPL [Member] |  |
Long-term Purchase Commitment [Line Items] |  |
Minimum future commitments | 130 |
Scenario, Forecast [Member] | Coal [Member] |  |
Long-term Purchase Commitment [Line Items] |  |
Minimum future commitments | 309 | [2]
Scenario, Forecast [Member] | Coal [Member] | IPL [Member] |  |
Long-term Purchase Commitment [Line Items] |  |
Minimum future commitments | 134 | [2]
Scenario, Forecast [Member] | Coal [Member] | WPL [Member] |  |
Long-term Purchase Commitment [Line Items] |  |
Minimum future commitments | 175 | [2]
Scenario, Forecast [Member] | SO2 emission allowances [Member] |  |
Long-term Purchase Commitment [Line Items] |  |
Minimum future commitments | 34 |
Scenario, Forecast [Member] | SO2 emission allowances [Member] | IPL [Member] |  |
Long-term Purchase Commitment [Line Items] |  |
Minimum future commitments | 34 |
Scenario, Forecast [Member] | SO2 emission allowances [Member] | WPL [Member] |  |
Long-term Purchase Commitment [Line Items] |  |
Minimum future commitments | 0 |
Scenario, Forecast [Member] | Purchased Power [Member] |  |
Long-term Purchase Commitment [Line Items] |  |
Minimum future commitments | 1,866 | [3]
Scenario, Forecast [Member] | Purchased Power [Member] | IPL [Member] |  |
Long-term Purchase Commitment [Line Items] |  |
Minimum future commitments | 1,620 | [3]
Scenario, Forecast [Member] | Purchased Power [Member] | WPL [Member] |  |
Long-term Purchase Commitment [Line Items] |  |
Minimum future commitments | 246 | [3]
Scenario, Forecast [Member] | Purchased Power [Member] | DAEC (IPL) [Member] |  |
Long-term Purchase Commitment [Line Items] |  |
Minimum future commitments | 1,619 | [3]
Scenario, Forecast [Member] | Purchased Power [Member] | DAEC (IPL) [Member] | IPL [Member] |  |
Long-term Purchase Commitment [Line Items] |  |
Minimum future commitments | 1,619 | [3]
Scenario, Forecast [Member] | Purchased Power [Member] | DAEC (IPL) [Member] | WPL [Member] |  |
Long-term Purchase Commitment [Line Items] |  |
Minimum future commitments | 0 | [3]
Scenario, Forecast [Member] | Purchased Power [Member] | Other [Member] |  |
Long-term Purchase Commitment [Line Items] |  |
Minimum future commitments | 247 | [3]
Scenario, Forecast [Member] | Purchased Power [Member] | Other [Member] | IPL [Member] |  |
Long-term Purchase Commitment [Line Items] |  |
Minimum future commitments | 1 | [3]
Scenario, Forecast [Member] | Purchased Power [Member] | Other [Member] | WPL [Member] |  |
Long-term Purchase Commitment [Line Items] |  |
Minimum future commitments | $ 246 | [3]
[1] | Includes individual commitments incurred during the normal course of business that exceeded $1 million at March 31, 2014.
[2] | Corporate Services entered into system-wide coal contracts on behalf of IPL and WPL that include minimum future commitments. These commitments were assigned to IPL and WPL based on information available as of March 31, 2014 regarding expected future usage, which is subject to change.
[3] | Includes payments required by PPAs for capacity rights and minimum quantities of MWhs required to be purchased.

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- Definition Individual commitments incurred in excess of $1 million + References No definition available. + Details
Name: | lnt_IndividualCommitmentsIncurred
Namespace Prefix: | lnt_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

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- Definition The minimum amount the entity agreed to spend under the long-term purchase commitment. + References No definition available. + Details
Name: | us-gaap_LongTermPurchaseCommitmentAmount
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

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- Details
Name: | us-gaap_LongTermPurchaseCommitmentLineItems
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration