XML 97 R51.htm IDEA: XBRL DOCUMENT
v2.4.1.9

Debt (Credit Facilities) (Details) (USD $) In Millions, unless otherwise specified | 3 Months Ended |
--- | --- | ---
Mar. 31, 2015 | Dec. 31, 2014
Commercial paper: |  |
Amount outstanding | $ 41.5 us-gaap_CommercialPaper | $ 141.3 us-gaap_CommercialPaper
Weighted average remaining maturity (in days) | 1 day |
Weighted average interest rates | 0.50%us-gaap_ShortTermDebtWeightedAverageInterestRate |
Available credit facility capacity | 958.5 us-gaap_LineOfCreditFacilityRemainingBorrowingCapacity |
Parent Company [Member] |  |
Commercial paper: |  |
Amount outstanding | 41.5 us-gaap_CommercialPaper / dei_LegalEntityAxis = us-gaap_ParentCompanyMember |
Weighted average remaining maturity (in days) | 1 day |
Weighted average interest rates | 0.50%us-gaap_ShortTermDebtWeightedAverageInterestRate / dei_LegalEntityAxis = us-gaap_ParentCompanyMember |
Available credit facility capacity | 258.5 us-gaap_LineOfCreditFacilityRemainingBorrowingCapacity / dei_LegalEntityAxis = us-gaap_ParentCompanyMember |
IPL [Member] |  |
Commercial paper: |  |
Amount outstanding | 0 us-gaap_CommercialPaper / dei_LegalEntityAxis = lnt_IplMember |
Available credit facility capacity | 300.0 us-gaap_LineOfCreditFacilityRemainingBorrowingCapacity / dei_LegalEntityAxis = lnt_IplMember |
WPL [Member] |  |
Commercial paper: |  |
Amount outstanding | 0 us-gaap_CommercialPaper / dei_LegalEntityAxis = lnt_WplMember |
Available credit facility capacity | $ 400.0 us-gaap_LineOfCreditFacilityRemainingBorrowingCapacity / dei_LegalEntityAxis = lnt_WplMember |

X
- Details
Name: | lnt_CommercialPaperAbstract
Namespace Prefix: | lnt_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

X
- Definition Short Term Debt Weighted Average Remaining Maturity + References No definition available. + Details
Name: | lnt_ShortTermDebtWeightedAverageRemainingMaturity
Namespace Prefix: | lnt_
Data Type: | xbrli:durationItemType
Balance Type: | na
Period Type: | duration

X
- Definition Carrying value as of the balance sheet date of short-term borrowings using unsecured obligations issued by banks, corporations and other borrowers to investors. The maturities of these money market securities generally do not exceed 270 days. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 03 -Paragraph 16 -Article 7 Reference 2: 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(a)(3)) -URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 942 -SubTopic 210 -Section S99 -Paragraph 1 -Subparagraph (SX 210.9-03.13(2)) -URI http://asc.fasb.org/extlink&oid=6876686&loc=d3e534808-122878 Reference 4: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 02 -Paragraph 19 -Subparagraph a(3) -Article 5 Reference 5: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 03 -Paragraph 13 -Subparagraph 2 -Article 9 + Details
Name: | us-gaap_CommercialPaper
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

X
- Definition Amount of borrowing capacity currently available under the credit facility (current borrowing capacity less the amount of borrowings outstanding). + 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 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 02 -Paragraph 19, 22 -Article 5 + Details
Name: | us-gaap_LineOfCreditFacilityRemainingBorrowingCapacity
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

X
- Definition Weighted average interest rate of short-term debt outstanding. + 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)) -URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 02 -Paragraph 19 -Subparagraph b -Article 5 + Details
Name: | us-gaap_ShortTermDebtWeightedAverageInterestRate
Namespace Prefix: | us-gaap_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | instant

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: | dei_LegalEntityAxis=us-gaap_ParentCompanyMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |