XML 170 R128.htm IDEA: XBRL DOCUMENT
v3.6.0.2

Commitments And Contingencies (Narrative) (Details) $ in Millions | 12 Months Ended
--- | ---
Dec. 31, 2016 USD ($)
Long-term Purchase Commitment [Line Items] |
Minimum future commitments | $ 2,400
Performance guarantees outstanding | 75
Present value abandonment obligation | $ 31
Workforce Subject to Collective Bargaining Arrangements [Member] |
Long-term Purchase Commitment [Line Items] |
Employees covered by collective bargaining agreement | 56.00%
Workforce Subject to Collective Bargaining Arrangements Expiring within One Year [Member] |
Long-term Purchase Commitment [Line Items] |
Employees covered by collective bargaining agreement | 19.00%
Capital Purchase Obligation [Member] |
Long-term Purchase Commitment [Line Items] |
Minimum future commitments | $ 58
IPL [Member] |
Long-term Purchase Commitment [Line Items] |
Minimum future commitments | 1,774
Maximum indemnification limit | $ 17
IPL [Member] | Workforce Subject to Collective Bargaining Arrangements [Member] |
Long-term Purchase Commitment [Line Items] |
Employees covered by collective bargaining agreement | 65.00%
IPL [Member] | Workforce Subject to Collective Bargaining Arrangements Expiring within One Year [Member] |
Long-term Purchase Commitment [Line Items] |
Employees covered by collective bargaining agreement | 46.00%
IPL [Member] | Capital Purchase Obligation [Member] |
Long-term Purchase Commitment [Line Items] |
Minimum future commitments | $ 3
WPL [Member] |
Long-term Purchase Commitment [Line Items] |
Minimum future commitments | $ 611
WPL [Member] | Workforce Subject to Collective Bargaining Arrangements [Member] |
Long-term Purchase Commitment [Line Items] |
Employees covered by collective bargaining agreement | 81.00%
WPL [Member] | Capital Purchase Obligation [Member] |
Long-term Purchase Commitment [Line Items] |
Minimum future commitments | $ 55
Environmental Issue [Member] | IPL [Member] |
Long-term Purchase Commitment [Line Items] |
Damages awarded | 6
Environmental Issue [Member] | WPL [Member] |
Long-term Purchase Commitment [Line Items] |
Damages awarded | $ 7

X
- Definition Performance Guarantees Outstanding + References No definition available. + Details
Name: | lnt_PerformanceGuaranteesOutstanding
Namespace Prefix: | lnt_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

X
- Definition Present value abandonment obligation + References No definition available. + Details
Name: | lnt_PresentValueAbandonmentObligation
Namespace Prefix: | lnt_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

X
- Definition For an entity that discloses a concentration risk in relation to quantitative amount, which serves as the "benchmark" (or denominator) in the equation, this concept represents the concentration percentage derived from the division. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 275 -SubTopic 10 -Section 50 -Paragraph 18 -URI http://asc.fasb.org/extlink&oid=64851502&loc=d3e6351-108592 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 825 -SubTopic 10 -Section 50 -Paragraph 20 -URI http://asc.fasb.org/extlink&oid=73719730&loc=d3e13531-108611 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 275 -SubTopic 10 -Section 50 -Paragraph 20 -URI http://asc.fasb.org/extlink&oid=64851502&loc=d3e6404-108592 Reference 4: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 825 -SubTopic 10 -Section 50 -Paragraph 21 -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=73719730&loc=d3e13537-108611 + Details
Name: | us-gaap_ConcentrationRiskPercentage1
Namespace Prefix: | us-gaap_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | duration

X
- Definition Maximum potential amount of future payments (undiscounted) the guarantor could be required to make under the guarantee or each group of similar guarantees before reduction for potential recoveries under recourse or collateralization provisions. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 460 -SubTopic 10 -Section 50 -Paragraph 4 -Subparagraph (b)(1) -URI http://asc.fasb.org/extlink&oid=6851643&loc=d3e12069-110248 + Details
Name: | us-gaap_GuaranteeObligationsMaximumExposure
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

X
- 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

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

X
- Definition Amount of damages awarded to the plaintiff in the legal matter. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 450 -SubTopic 20 -Section 50 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=25496072&loc=d3e14326-108349 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 450 -SubTopic 20 -Section 50 -Paragraph 4 -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=25496072&loc=d3e14435-108349 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 450 -SubTopic 20 -Section 50 -Paragraph 9 -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=25496072&loc=d3e14557-108349 + Details
Name: | us-gaap_LossContingencyDamagesAwardedValue
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- Details
Name: | us-gaap_ConcentrationRiskByBenchmarkAxis=us-gaap_WorkforceSubjectToCollectiveBargainingArrangementsMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_ConcentrationRiskByBenchmarkAxis=us-gaap_WorkforceSubjectToCollectiveBargainingArrangementsExpiringWithinOneYearMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_LongTermPurchaseCommitmentByCategoryOfItemPurchasedAxis=lnt_CapitalPurchaseObligationMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | dei_LegalEntityAxis=lnt_IplMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | dei_LegalEntityAxis=lnt_WplMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_LitigationCaseAxis=us-gaap_EnvironmentalIssueMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |