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Debt (Narrative) (Details) | Dec. 31, 2016 USD ($) revolving_credit_facility
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Debt Instrument [Line Items] |
Number of revolving credit facilities included in short-term borrowing arrangements (number of facilities) | revolving_credit_facility | 3
Line of credit facility, current borrowing capacity | $ 1,000,000,000
Non-recourse debt and hybrid securities consolidated capital maximum limit | 15.00%
Parent Company [Member] |
Debt Instrument [Line Items] |
Line of credit facility, current borrowing capacity | $ 300,000,000
IPL [Member] |
Debt Instrument [Line Items] |
Line of credit facility, current borrowing capacity | 300,000,000
WPL [Member] |
Debt Instrument [Line Items] |
Line of credit facility, current borrowing capacity | $ 400,000,000

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- Definition Hybrid Securities Maximum Limit + References No definition available. + Details
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Namespace Prefix: | lnt_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | instant

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- Definition Number of Short-Term Debt Instruments, Revolving Credit Facilities + References No definition available. + Details
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Namespace Prefix: | lnt_
Data Type: | xbrli:integerItemType
Balance Type: | na
Period Type: | instant

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- Definition Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table. + References No definition available. + Details
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Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

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- Definition Amount of current borrowing capacity under the credit facility considering any current restrictions on the amount that could be borrowed (for example, borrowings may be limited by the amount of current assets), but without considering any amounts currently outstanding under the facility. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02.19(b),22(b)) -URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682 + Details
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Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

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- Details
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Namespace Prefix: |
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Period Type: |

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- Details
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Namespace Prefix: |
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Period Type: |

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- Details
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Namespace Prefix: |
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Balance Type: |
Period Type: |