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Regulatory Matters (Narrative) (Details) - USD ($) $ in Millions | Sep. 30, 2021 | Dec. 31, 2020
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Regulatory Matters [Line Items] |  |
Regulatory assets | $ 2,018 | $ 2,010
IPL [Member] |  |
Regulatory Matters [Line Items] |  |
Regulatory assets | 1,507 | 1,483
WPL [Member] |  |
Regulatory Matters [Line Items] |  |
Regulatory assets | 511 | $ 527
Deferred Fuel Costs | IPL [Member] |  |
Regulatory Matters [Line Items] |  |
Regulatory assets | 15 |
Deferred Fuel Costs | WPL [Member] |  |
Regulatory Matters [Line Items] |  |
Regulatory assets | $ 12 |

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- Definition Regulatory Matters [Line Items] + References No definition available. + Details
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- Definition The amount for the individual regulatory asset as itemized in a table of regulatory assets as of the end of the period. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 980 -SubTopic 340 -Section 50 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=6499975&loc=d3e44250-110382 + Details
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- Details
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- Details
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