XML 122 R93.htm IDEA: XBRL DOCUMENT
v3.20.4

Benefit Plans (Amounts Recognized On The Consolidated Balance Sheets) (Details) - USD ($) $ in Millions | Dec. 31, 2020 | Dec. 31, 2019
--- | --- | ---
Amounts recognized on the balance sheets consist of: |  |
Pension and other benefit obligations | $ (511) | $ (484)
Pension Plans, Defined Benefit [Member] |  |
Amounts recognized on the balance sheets consist of: |  |
Non-current assets | 0 | 0
Current liabilities | (2) | (14)
Pension and other benefit obligations | (365) | (335)
Net amounts recognized at December 31 | (367) | (349)
Amounts recognized in Regulatory Assets consist of: |  |
Net actuarial loss | 533 | 485
Prior service credit | (5) | (5)
Net amount recognized at December 31 | 528 | 480
Other Postretirement Benefits Plans [Member] |  |
Amounts recognized on the balance sheets consist of: |  |
Non-current assets | 8 | 10
Current liabilities | (8) | (8)
Pension and other benefit obligations | (119) | (111)
Net amounts recognized at December 31 | (119) | (109)
Amounts recognized in Regulatory Assets consist of: |  |
Net actuarial loss | 54 | 45
Prior service credit | (1) | (1)
Net amount recognized at December 31 | 53 | 44
IPL [Member] |  |
Amounts recognized on the balance sheets consist of: |  |
Pension and other benefit obligations | (186) | (168)
IPL [Member] | Pension Plans, Defined Benefit [Member] |  |
Amounts recognized on the balance sheets consist of: |  |
Non-current assets | 0 | 0
Current liabilities | (1) | (1)
Pension and other benefit obligations | (161) | (144)
Net amounts recognized at December 31 | (162) | (145)
Amounts recognized in Regulatory Assets consist of: |  |
Net actuarial loss | 228 | 208
Prior service credit | (1) | (1)
Net amount recognized at December 31 | 227 | 207
IPL [Member] | Other Postretirement Benefits Plans [Member] |  |
Amounts recognized on the balance sheets consist of: |  |
Non-current assets | 4 | 7
Current liabilities | (2) | (2)
Pension and other benefit obligations | (19) | (19)
Net amounts recognized at December 31 | (17) | (14)
Amounts recognized in Regulatory Assets consist of: |  |
Net actuarial loss | 20 | 17
Prior service credit | 0 | 0
Net amount recognized at December 31 | 20 | 17
WPL [Member] |  |
Amounts recognized on the balance sheets consist of: |  |
Pension and other benefit obligations | (222) | (211)
WPL [Member] | Pension Plans, Defined Benefit [Member] |  |
Amounts recognized on the balance sheets consist of: |  |
Non-current assets | 0 | 0
Current liabilities | 0 | 0
Pension and other benefit obligations | (152) | (144)
Net amounts recognized at December 31 | (152) | (144)
Amounts recognized in Regulatory Assets consist of: |  |
Net actuarial loss | 233 | 212
Prior service credit | (1) | (1)
Net amount recognized at December 31 | 232 | 211
WPL [Member] | Other Postretirement Benefits Plans [Member] |  |
Amounts recognized on the balance sheets consist of: |  |
Non-current assets | 3 | 3
Current liabilities | (6) | (6)
Pension and other benefit obligations | (68) | (65)
Net amounts recognized at December 31 | (71) | (68)
Amounts recognized in Regulatory Assets consist of: |  |
Net actuarial loss | 25 | 22
Prior service credit | (1) | (1)
Net amount recognized at December 31 | $ 24 | $ 21

X
- Definition Defined benefit plan amounts recognized in regulatory asset and regulatory liability and other comprehensive income net gain loss before tax. + References No definition available. + Details
Name: | lnt_DefinedBenefitPlanAmountsRecognizedInRegulatoryAssetAndRegulatoryLiabilityAndOtherComprehensiveIncomeNetGainLossBeforeTax
Namespace Prefix: | lnt_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

X
- Definition Defined Benefit Plan Amounts Recognized In Regulatory Asset And Regulatory Liability And Other Comprehensive Income Net Prior Service Cost Credit Before Tax + References No definition available. + Details
Name: | lnt_DefinedBenefitPlanAmountsRecognizedInRegulatoryAssetAndRegulatoryLiabilityAndOtherComprehensiveIncomeNetPriorServiceCostCreditBeforeTax
Namespace Prefix: | lnt_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition Defined Benefit Plan, Amounts Recognized in Regulatory Assets, Regulatory Liabilities, and Accumulated Other Comprehensive Income (Loss) [Abstract] + References No definition available. + Details
Name: | lnt_DefinedBenefitPlanAmountsRecognizedInRegulatoryAssetsRegulatoryLiabilitiesAndAccumulatedOtherComprehensiveIncomeLossAbstract
Namespace Prefix: | lnt_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

X
- Definition Defined Benefit Plan Amounts Recognized In Regulatory Assets Regulatory Liabilities And Other Comprehensive Income + References No definition available. + Details
Name: | lnt_DefinedBenefitPlanAmountsRecognizedInRegulatoryAssetsRegulatoryLiabilitiesAndOtherComprehensiveIncome
Namespace Prefix: | lnt_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition Pension and other postretirement defined benefit plans non-current assets. + References No definition available. + Details
Name: | lnt_PensionAndOtherPostretirementDefinedBenefitPlansNonCurrentAssets
Namespace Prefix: | lnt_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition Amount of asset (liability), recognized in statement of financial position, for defined benefit pension and other postretirement plans. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (c) -URI http://asc.fasb.org/extlink&oid=118255775&loc=d3e1928-114920 Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 45 -Paragraph 2 -URI http://asc.fasb.org/extlink&oid=109237824&loc=d3e1703-114919 + Details
Name: | us-gaap_DefinedBenefitPlanAmountsRecognizedInBalanceSheet
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- References No definition available. + Details
Name: | us-gaap_DefinedBenefitPlanAmountsRecognizedInBalanceSheetAbstract
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

X
- Definition Amount of liability, recognized in statement of financial position, for defined benefit pension and other postretirement plans, classified as current. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 45 -Paragraph 3 -URI http://asc.fasb.org/extlink&oid=109237824&loc=d3e1731-114919 Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (c) -URI http://asc.fasb.org/extlink&oid=118255775&loc=d3e1928-114920 Reference 3: http://www.xbrl.org/2003/role/exampleRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 55 -Paragraph 17 -URI http://asc.fasb.org/extlink&oid=118257860&loc=d3e4179-114921 Reference 4: 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(20)) -URI http://asc.fasb.org/extlink&oid=120391452&loc=d3e13212-122682 Reference 5: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 45 -Paragraph 2 -URI http://asc.fasb.org/extlink&oid=109237824&loc=d3e1703-114919 + Details
Name: | us-gaap_PensionAndOtherPostretirementDefinedBenefitPlansCurrentLiabilities
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

X
- Definition Amount of liability, recognized in statement of financial position, for defined benefit pension and other postretirement plans, classified as noncurrent. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 45 -Paragraph 2 -URI http://asc.fasb.org/extlink&oid=109237824&loc=d3e1703-114919 Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 45 -Paragraph 3 -URI http://asc.fasb.org/extlink&oid=109237824&loc=d3e1731-114919 Reference 3: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (c) -URI http://asc.fasb.org/extlink&oid=118255775&loc=d3e1928-114920 Reference 4: http://www.xbrl.org/2003/role/exampleRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 55 -Paragraph 17 -URI http://asc.fasb.org/extlink&oid=118257860&loc=d3e4179-114921 Reference 5: 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(24)) -URI http://asc.fasb.org/extlink&oid=120391452&loc=d3e13212-122682 + Details
Name: | us-gaap_PensionAndOtherPostretirementDefinedBenefitPlansLiabilitiesNoncurrent
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

X
- Details
Name: | us-gaap_RetirementPlanTypeAxis=us-gaap_PensionPlansDefinedBenefitMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_RetirementPlanTypeAxis=us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember
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: |