XML 117 R83.htm IDEA: XBRL DOCUMENT
v3.8.0.1

Debt (Long-term Debt) (Details) - USD ($) $ in Millions | 12 Months Ended |
--- | --- | ---
Dec. 31, 2017 | Dec. 31, 2016
Debt Instrument [Line Items] |  |  |
Long-term debt |  | $ 4,902.5 | $ 4,357.1
Current maturities |  | (855.7) | (4.6)
Unamortized debt issuance costs |  | (25.4) | (23.4)
Unamortized debt (discount) and premium, net |  | (10.8) | (13.5)
Long-term debt, net | [1] | 4,010.6 | 4,315.6
Senior Debentures [Member] |  |  |
Debt Instrument [Line Items] |  |  |
Long-term debt | [2] | 2,425.0 | 2,175.0
Senior Debentures [Member] | 5.875% senior debenture, due 2018 [Member] |  |  |
Debt Instrument [Line Items] |  |  |
Long-term debt | [2] | $ 100.0 | $ 100.0
Interest rate |  | 5.875% | 5.875%
Senior Debentures [Member] | 7.25% senior debenture, due 2018 [Member] |  |  |
Debt Instrument [Line Items] |  |  |
Long-term debt | [2] | $ 250.0 | $ 250.0
Interest rate |  | 7.25% | 7.25%
Senior Debentures [Member] | 3.65% senior debenture, due 2020 [Member] |  |  |
Debt Instrument [Line Items] |  |  |
Long-term debt | [2] | $ 200.0 | $ 200.0
Interest rate |  | 3.65% | 3.65%
Senior Debentures [Member] | 3.25% senior debenture, due 2024 [Member] |  |  |
Debt Instrument [Line Items] |  |  |
Long-term debt | [2],[3] | $ 500.0 | $ 250.0
Interest rate |  | 3.25% | 3.25%
Senior Debentures [Member] | 3.4% senior debenture, due 2025 [Member] |  |  |
Debt Instrument [Line Items] |  |  |
Long-term debt | [2] | $ 250.0 | $ 250.0
Interest rate |  | 3.40% | 3.40%
Senior Debentures [Member] | 5.5% senior debenture, due 2025 [Member] |  |  |
Debt Instrument [Line Items] |  |  |
Long-term debt | [2] | $ 50.0 | $ 50.0
Interest rate |  | 5.50% | 5.50%
Senior Debentures [Member] | 6.45% senior debenture, due 2033 [Member] |  |  |
Debt Instrument [Line Items] |  |  |
Long-term debt | [2] | $ 100.0 | $ 100.0
Interest rate |  | 6.45% | 6.45%
Senior Debentures [Member] | 6.3% senior debenture, due 2034 [Member] |  |  |
Debt Instrument [Line Items] |  |  |
Long-term debt | [2] | $ 125.0 | $ 125.0
Interest rate |  | 6.30% | 6.30%
Senior Debentures [Member] | 6.25% senior debenture, due 2039 [Member] |  |  |
Debt Instrument [Line Items] |  |  |
Long-term debt | [2] | $ 300.0 | $ 300.0
Interest rate |  | 6.25% | 6.25%
Senior Debentures [Member] | 4.7% senior debenture, due 2043 [Member] |  |  |
Debt Instrument [Line Items] |  |  |
Long-term debt | [2] | $ 250.0 | $ 250.0
Interest rate |  | 4.70% | 4.70%
Senior Debentures [Member] | 3.7% senior debenture, due 2046 [Member] |  |  |
Debt Instrument [Line Items] |  |  |
Long-term debt | [2] | $ 300.0 | $ 300.0
Interest rate |  | 3.70% | 3.70%
Debentures [Member] |  |  |
Debt Instrument [Line Items] |  |  |
Long-term debt | [2] | $ 1,850.0 | $ 1,550.0
Debentures [Member] | 5% debenture, due 2019 [Member] |  |  |
Debt Instrument [Line Items] |  |  |
Long-term debt | [2] | $ 250.0 | $ 250.0
Interest rate |  | 5.00% | 5.00%
Debentures [Member] | 4.6% debenture, due 2020 [Member] |  |  |
Debt Instrument [Line Items] |  |  |
Long-term debt | [2] | $ 150.0 | $ 150.0
Interest rate |  | 4.60% | 4.60%
Debentures [Member] | 2.25% debenture, due 2022 [Member] |  |  |
Debt Instrument [Line Items] |  |  |
Long-term debt | [2] | $ 250.0 | $ 250.0
Interest rate |  | 2.25% | 2.25%
Debentures [Member] | 3.05% debenture, due 2027 [Member] |  |  |
Debt Instrument [Line Items] |  |  |
Long-term debt | [2],[4] | $ 300.0 |
Interest rate |  | 3.05% |
Debentures [Member] | 6.25% debenture, due 2034 [Member] |  |  |
Debt Instrument [Line Items] |  |  |
Long-term debt | [2] | $ 100.0 | $ 100.0
Interest rate |  | 6.25% | 6.25%
Debentures [Member] | 6.375% debenture, due 2037 [Member] |  |  |
Debt Instrument [Line Items] |  |  |
Long-term debt | [2] | $ 300.0 | $ 300.0
Interest rate |  | 6.375% | 6.375%
Debentures [Member] | 7.6% debenture, due 2038 [Member] |  |  |
Debt Instrument [Line Items] |  |  |
Long-term debt | [2] | $ 250.0 | $ 250.0
Interest rate |  | 7.60% | 7.60%
Debentures [Member] | 4.1% debenture, due 2044 [Member] |  |  |
Debt Instrument [Line Items] |  |  |
Long-term debt | [2] | $ 250.0 | $ 250.0
Interest rate |  | 4.10% | 4.10%
Other Long Term Debt [Member] |  |  |
Debt Instrument [Line Items] |  |  |
Long-term debt |  | $ 627.5 | $ 632.1
Other [Member] | Other, 1% at December 31, 2017, due 2018 to 2025 [Member] |  |  |
Debt Instrument [Line Items] |  |  |
Long-term debt |  | $ 2.9 | 3.3
Interest rate |  | 1.00% |
IPL [Member] |  |  |
Debt Instrument [Line Items] |  |  |
Long-term debt |  | $ 2,425.0 | 2,175.0
Current maturities |  | (350.0) | 0.0
Unamortized debt issuance costs |  | (14.3) | (13.7)
Unamortized debt (discount) and premium, net |  | (4.7) | (7.8)
Long-term debt, net | [1] | 2,056.0 | 2,153.5
IPL [Member] | Senior Debentures [Member] |  |  |
Debt Instrument [Line Items] |  |  |
Long-term debt | [2] | 2,425.0 | 2,175.0
IPL [Member] | Senior Debentures [Member] | 5.875% senior debenture, due 2018 [Member] |  |  |
Debt Instrument [Line Items] |  |  |
Long-term debt | [2] | $ 100.0 | $ 100.0
Interest rate |  | 5.875% | 5.875%
IPL [Member] | Senior Debentures [Member] | 7.25% senior debenture, due 2018 [Member] |  |  |
Debt Instrument [Line Items] |  |  |
Long-term debt | [2] | $ 250.0 | $ 250.0
Interest rate |  | 7.25% | 7.25%
IPL [Member] | Senior Debentures [Member] | 3.65% senior debenture, due 2020 [Member] |  |  |
Debt Instrument [Line Items] |  |  |
Long-term debt | [2] | $ 200.0 | $ 200.0
Interest rate |  | 3.65% | 3.65%
IPL [Member] | Senior Debentures [Member] | 3.25% senior debenture, due 2024 [Member] |  |  |
Debt Instrument [Line Items] |  |  |
Long-term debt | [2],[3] | $ 500.0 | $ 250.0
Proceeds from the issuance of debt |  | $ 250.0 |
Interest rate |  | 3.25% | 3.25%
IPL [Member] | Senior Debentures [Member] | 3.4% senior debenture, due 2025 [Member] |  |  |
Debt Instrument [Line Items] |  |  |
Long-term debt | [2] | $ 250.0 | $ 250.0
Interest rate |  | 3.40% | 3.40%
IPL [Member] | Senior Debentures [Member] | 5.5% senior debenture, due 2025 [Member] |  |  |
Debt Instrument [Line Items] |  |  |
Long-term debt | [2] | $ 50.0 | $ 50.0
Interest rate |  | 5.50% | 5.50%
IPL [Member] | Senior Debentures [Member] | 6.45% senior debenture, due 2033 [Member] |  |  |
Debt Instrument [Line Items] |  |  |
Long-term debt | [2] | $ 100.0 | $ 100.0
Interest rate |  | 6.45% | 6.45%
IPL [Member] | Senior Debentures [Member] | 6.3% senior debenture, due 2034 [Member] |  |  |
Debt Instrument [Line Items] |  |  |
Long-term debt | [2] | $ 125.0 | $ 125.0
Interest rate |  | 6.30% | 6.30%
IPL [Member] | Senior Debentures [Member] | 6.25% senior debenture, due 2039 [Member] |  |  |
Debt Instrument [Line Items] |  |  |
Long-term debt | [2] | $ 300.0 | $ 300.0
Interest rate |  | 6.25% | 6.25%
IPL [Member] | Senior Debentures [Member] | 4.7% senior debenture, due 2043 [Member] |  |  |
Debt Instrument [Line Items] |  |  |
Long-term debt | [2] | $ 250.0 | $ 250.0
Interest rate |  | 4.70% | 4.70%
IPL [Member] | Senior Debentures [Member] | 3.7% senior debenture, due 2046 [Member] |  |  |
Debt Instrument [Line Items] |  |  |
Long-term debt | [2] | $ 300.0 | $ 300.0
Interest rate |  | 3.70% | 3.70%
WPL [Member] |  |  |
Debt Instrument [Line Items] |  |  |
Long-term debt |  | $ 1,850.0 | $ 1,550.0
Current maturities |  | 0.0 | 0.0
Unamortized debt issuance costs |  | (10.5) | (9.1)
Unamortized debt (discount) and premium, net |  | (6.1) | (5.7)
Long-term debt, net | [1] | 1,833.4 | 1,535.2
WPL [Member] | Debentures [Member] |  |  |
Debt Instrument [Line Items] |  |  |
Long-term debt | [2] | 1,850.0 | 1,550.0
WPL [Member] | Debentures [Member] | 5% debenture, due 2019 [Member] |  |  |
Debt Instrument [Line Items] |  |  |
Long-term debt | [2] | $ 250.0 | $ 250.0
Interest rate |  | 5.00% | 5.00%
WPL [Member] | Debentures [Member] | 4.6% debenture, due 2020 [Member] |  |  |
Debt Instrument [Line Items] |  |  |
Long-term debt | [2] | $ 150.0 | $ 150.0
Interest rate |  | 4.60% | 4.60%
WPL [Member] | Debentures [Member] | 2.25% debenture, due 2022 [Member] |  |  |
Debt Instrument [Line Items] |  |  |
Long-term debt | [2] | $ 250.0 | $ 250.0
Interest rate |  | 2.25% | 2.25%
WPL [Member] | Debentures [Member] | 3.05% debenture, due 2027 [Member] |  |  |
Debt Instrument [Line Items] |  |  |
Long-term debt | [2],[4] | $ 300.0 |
Proceeds from the issuance of debt | [2] | $ 300.0 |
Interest rate |  | 3.05% |
WPL [Member] | Debentures [Member] | 6.25% debenture, due 2034 [Member] |  |  |
Debt Instrument [Line Items] |  |  |
Long-term debt | [2] | $ 100.0 | $ 100.0
Interest rate |  | 6.25% | 6.25%
WPL [Member] | Debentures [Member] | 6.375% debenture, due 2037 [Member] |  |  |
Debt Instrument [Line Items] |  |  |
Long-term debt | [2] | $ 300.0 | $ 300.0
Interest rate |  | 6.375% | 6.375%
WPL [Member] | Debentures [Member] | 7.6% debenture, due 2038 [Member] |  |  |
Debt Instrument [Line Items] |  |  |
Long-term debt | [2] | $ 250.0 | $ 250.0
Interest rate |  | 7.60% | 7.60%
WPL [Member] | Debentures [Member] | 4.1% debenture, due 2044 [Member] |  |  |
Debt Instrument [Line Items] |  |  |
Long-term debt | [2] | $ 250.0 | $ 250.0
Interest rate |  | 4.10% | 4.10%
Alliant Energy Finance, LLC [Member] | Term Loan Credit Agreement [Member] | Term loan credit agreement through 2018, 2% at December 31, 2017 [Member] |  |  |
Debt Instrument [Line Items] |  |  |
Long-term debt | [5] | $ 500.0 | $ 500.0
Interest rate |  | 2.00% |
Corporate Services [Member] | Senior Notes [Member] | 3.45% senior notes, due 2022 [Member] |  |  |
Debt Instrument [Line Items] |  |  |
Long-term debt | [2] | $ 75.0 | $ 75.0
Interest rate |  | 3.45% | 3.45%
Sheboygan Power, LLC [Member] | Senior Secured Notes [Member] | 5.06% senior secured notes, due 2018 to 2024 [Member] |  |  |
Debt Instrument [Line Items] |  |  |
Long-term debt | [2] | $ 49.6 | $ 53.8
Interest rate |  | 5.06% | 5.06%
[1] | There were no significant sinking fund requirements related to the outstanding long-term debt.
[2] | Contains optional redemption provisions which, if elected by the issuer at its sole discretion, could require material redemption premium payments by the issuer. The redemption premium payments under these optional redemption provisions are variable and dependent on applicable U.S. Treasury rates at the time of redemption.
[3] | In 2017, IPL issued $250 million of 3.25% senior debentures due 2024. The proceeds from the issuance were used by IPL to reduce commercial paper classified as long-term debt, reduce cash amounts received from its sales of accounts receivable program and for general corporate purposes.
[4] | In 2017, WPL issued $300 million of 3.05% debentures due 2027. The proceeds from the issuance were used by WPL to reduce commercial paper and for general corporate purposes.
[5] | Refer to Note 9(a) for discussion of a financial covenant contained in AEF’s term loan credit agreement.

X
- Definition Amount, before unamortized (discount) premium and debt issuance costs, of long-term debt. Includes, but is not limited to, notes payable, bonds payable, commercial loans, mortgage loans, convertible debt, subordinated debt and other types of debt. + 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(22)) -URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 944 -SubTopic 210 -Section S99 -Paragraph 1 -Subparagraph (SX 210.7-03(16)) -URI http://asc.fasb.org/extlink&oid=6879938&loc=d3e572229-122910 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(16)) -URI http://asc.fasb.org/extlink&oid=6876686&loc=d3e534808-122878 + Details
Name: | us-gaap_DebtInstrumentCarryingAmount
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

X
- Definition Contractual interest rate for funds borrowed, under the debt agreement. + 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 210.5-02.22(a)(1)) -URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682 + Details
Name: | us-gaap_DebtInstrumentInterestRateStatedPercentage
Namespace Prefix: | us-gaap_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | instant

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_DebtInstrumentLineItems
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

X
- Definition Amount, after accumulated amortization, of debt discount (premium). + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 835 -SubTopic 30 -Section 45 -Paragraph 4 -URI http://asc.fasb.org/extlink&oid=64930785&loc=d3e28567-108399 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 835 -SubTopic 30 -Section 45 -Paragraph 1A -URI http://asc.fasb.org/extlink&oid=64930785&loc=d3e28541-108399 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 835 -SubTopic 30 -Section 55 -Paragraph 8 -URI http://asc.fasb.org/extlink&oid=64930739&loc=d3e28878-108400 Reference 4: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 835 -SubTopic 30 -Section 45 -Paragraph 2 -URI http://asc.fasb.org/extlink&oid=64930785&loc=d3e28551-108399 Reference 5: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 835 -SubTopic 30 -Section 45 -Paragraph 3 -URI http://asc.fasb.org/extlink&oid=64930785&loc=d3e28555-108399 + Details
Name: | us-gaap_DebtInstrumentUnamortizedDiscountPremiumNet
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition Amount, after accumulated amortization, of debt issuance costs. Includes, but is not limited to, legal, accounting, underwriting, printing, and registration costs. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 835 -SubTopic 30 -Section 45 -Paragraph 3 -URI http://asc.fasb.org/extlink&oid=64930785&loc=d3e28555-108399 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 210.5-02.17) -URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682 + Details
Name: | us-gaap_DeferredFinanceCostsNet
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition Amount, after unamortized (discount) premium and debt issuance costs, of long-term debt, classified as current. Includes, but not limited to, notes payable, bonds payable, debentures, mortgage loans and commercial paper. Excludes capital lease obligations. + 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 210.5-02.19,20) -URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682 + Details
Name: | us-gaap_LongTermDebtCurrent
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

X
- Definition Amount after unamortized (discount) premium and debt issuance costs of long-term debt classified as noncurrent and excluding amounts to be repaid within one year or the normal operating cycle, if longer. Includes, but not limited to, notes payable, bonds payable, debentures, mortgage loans and commercial paper. Excludes capital lease obligations. + 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 210.5-02.22) -URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682 + Details
Name: | us-gaap_LongTermDebtNoncurrent
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

X
- Definition The cash inflow during the period from additional borrowings in aggregate debt. Includes proceeds from short-term and long-term debt. + References No definition available. + Details
Name: | us-gaap_ProceedsFromIssuanceOfDebt
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- Details
Name: | us-gaap_LongtermDebtTypeAxis=lnt_SeniorDebenturesMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_DebtInstrumentAxis=lnt_FivePointEightSevenFivePercentSeniorDebenturesDueTwoThousandEighteenMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_DebtInstrumentAxis=lnt_SevenPointTwoFivePercentSeniorDebenturesDueTwoThousandEighteenMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_DebtInstrumentAxis=lnt_ThreePointSixFivePercentSeniorDebenturesDueTwoThousandTwentyMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_DebtInstrumentAxis=lnt_ThreePointTwoFivePercentSeniorDebenturesDueTwoThousandTwentyFourMemberDomain
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_DebtInstrumentAxis=lnt_ThreePointFourPercentSeniorDebenturesDueTwoThousandTwentyFiveMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_DebtInstrumentAxis=lnt_FivePointFivePercentSeniorDebenturesDueTwoThousandTwentyFiveMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_DebtInstrumentAxis=lnt_SixPointFourFivePercentSeniorDebenturesDueTwoThousandThirtyThreeMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_DebtInstrumentAxis=lnt_SixPointThreePercentSeniorDebenturesDueTwoThousandThirtyFourMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_DebtInstrumentAxis=lnt_SixPointTwoFivePercentSeniorDebenturesDueTwoThousandThirtyNineMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_DebtInstrumentAxis=lnt_FourPointSevenPercentSeniorDebenturesDueTwoThousandFortyThreeMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_DebtInstrumentAxis=lnt_ThreePointSevenPercentSeniorDebenturesDueTwoThousandFortySixMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_LongtermDebtTypeAxis=lnt_DebenturesMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_DebtInstrumentAxis=lnt_FivePercentDebentureDueTwoThousandNineteenMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_DebtInstrumentAxis=lnt_FourPointSixPercentDebentureDueTwoThousandTwentyMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_DebtInstrumentAxis=lnt_TwoPointTwoFivePercentDebentureDueTwoThousandTwentyMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_DebtInstrumentAxis=lnt_ThreePointZeroFiveDebentureDueTwoThousandAndTwentySevenMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_DebtInstrumentAxis=lnt_SixPointTwoFivePercentDebentureDueTwoThousandThirtyFourMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_DebtInstrumentAxis=lnt_SixPointThreeSevenFivePercentDebentureDueTwoThousandThirtySevenMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_DebtInstrumentAxis=lnt_SevenPointSixPercentDebentureDueTwoThousandThirtyEightMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_DebtInstrumentAxis=lnt_FourPointOnePercentDebentureDueTwoThousandFortyFourMemberMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_LongtermDebtTypeAxis=lnt_OtherLongTermDebtMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_LongtermDebtTypeAxis=lnt_OtherLongTermDebtMiscellaneousMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_DebtInstrumentAxis=lnt_OnePercentAtDecemberThirtyFirstTwoThousandThirteenOtherLongTermDebtDueTwoThousandFourteenToTwoThousandTwentyFiveMember
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: | dei_LegalEntityAxis=lnt_AlliantEnergyFinanceLLCMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_LongtermDebtTypeAxis=lnt_TermLoanCreditAgreementMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_DebtInstrumentAxis=lnt_TermLoanCreditAgreementThroughOctoberTwentyEighteenMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

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

X
- Details
Name: | us-gaap_LongtermDebtTypeAxis=us-gaap_SeniorNotesMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_DebtInstrumentAxis=lnt_ThreePointFourFivePercentSeniorNotesDueTwoThousandTwentyTwoMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

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

X
- Details
Name: | us-gaap_LongtermDebtTypeAxis=lnt_SeniorSecuredNotesMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_DebtInstrumentAxis=lnt_FivePointZeroSixPercentOtherSeniorNotesDueTwoThousandTwelveToTwoThousandTwentyFourMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |