XML 72 R49.htm IDEA: XBRL DOCUMENT
v3.20.2

Debt (Narrative) (Details) - USD ($) $ in Millions | 1 Months Ended | 6 Months Ended
--- | --- | ---
Jun. 30, 2020 | Apr. 30, 2020 | Mar. 31, 2020 | Jun. 30, 2020 | Jun. 30, 2019
Debt [Line Items] |  |  |  |  |
Payments to retire long-term debt |  |  |  | $ 653.7 | $ 3.4
IPL [Member] |  |  |  |  |
Debt [Line Items] |  |  |  |  |
Payments to retire long-term debt |  |  |  | 200.0 | 0.0
WPL [Member] |  |  |  |  |
Debt [Line Items] |  |  |  |  |
Payments to retire long-term debt |  |  |  | $ 150.0 | $ 0.0
Term Loan Credit Agreement [Member] | Term Loan Credit Agreement Through March 2022 [Member] | Alliant Energy Finance, LLC [Member] |  |  |  |  |
Debt [Line Items] |  |  |  |  |
Proceeds from issuance of long-term debt |  |  | $ 300.0 |  |
Interest rate, percent | 1.00% |  |  | 1.00% |
Term Loan Credit Agreement [Member] | Term Loan Credit Agreement Through April 2020 [Member] | Alliant Energy Finance, LLC [Member] |  |  |  |  |
Debt [Line Items] |  |  |  |  |
Payments to retire long-term debt |  |  | $ 300.0 |  |
Debentures [Member] | 3.65% debenture, due 2050 [Member] | WPL [Member] |  |  |  |  |
Debt [Line Items] |  |  |  |  |
Proceeds from issuance of long-term debt |  | $ 350.0 |  |  |
Interest rate, percent |  | 3.65% |  |  |
Debentures [Member] | 4.6% debenture, due 2020 [Member] | WPL [Member] |  |  |  |  |
Debt [Line Items] |  |  |  |  |
Interest rate, percent | 4.60% |  |  | 4.60% |
Payments to retire long-term debt | $ 150.0 |  |  |  |
Senior Debentures [Member] | 2.3% senior debenture, due 2030 [Member] | IPL [Member] |  |  |  |  |
Debt [Line Items] |  |  |  |  |
Proceeds from issuance of long-term debt | $ 400.0 |  |  |  |
Interest rate, percent | 2.30% |  |  | 2.30% |
Senior Debentures [Member] | 3.65% senior debenture, due 2020 [Member] | IPL [Member] |  |  |  |  |
Debt [Line Items] |  |  |  |  |
Interest rate, percent | 3.65% |  |  | 3.65% |
Payments to retire long-term debt | $ 200.0 |  |  |  |

X
- Definition Contractual interest rate for funds borrowed, under the debt agreement. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -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 The cash inflow during the period from additional borrowings in aggregate debt. Includes proceeds from short-term and long-term debt. + References Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef -Publisher FASB -Name Accounting Standards Codification -Topic 230 -SubTopic 10 -Section 45 -Paragraph 14 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=118932676&loc=d3e3255-108585 + Details
Name: | us-gaap_ProceedsFromIssuanceOfDebt
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- Definition The cash outflow for debt initially having maturity due after one year or beyond the normal operating cycle, if longer. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 230 -SubTopic 10 -Section 45 -Paragraph 15 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=118932676&loc=d3e3291-108585 + Details
Name: | us-gaap_RepaymentsOfLongTermDebt
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

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_LongtermDebtTypeAxis=lnt_TermLoanCreditAgreementMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_DebtInstrumentAxis=lnt_TermLoanCreditAgreementThroughMarchTwoThousandTwentyTwoMember
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_DebtInstrumentAxis=lnt_TermLoanCreditAgreementThroughAprilTwoThousandandTwentyMember
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_ThreePointSixFivePercentDebenturesDueTwoThousandFiftyMember
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_LongtermDebtTypeAxis=lnt_SeniorDebenturesMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_DebtInstrumentAxis=lnt_TwoPointThreePercentSeniorDebenturesDueTwoThousandThirtyMember
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: |