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Regulatory Matters (Regulatory Assets) (Details) - USD ($) $ in Millions | Sep. 30, 2020 | Dec. 31, 2019
--- | --- | ---
Regulatory Assets [Line Items] |  |
Regulatory assets | $ 1,836 | $ 1,845
Tax-related [Member] |  |
Regulatory Assets [Line Items] |  |
Regulatory assets | 877 | 818
Pension and OPEB costs [Member] |  |
Regulatory Assets [Line Items] |  |
Regulatory assets | 492 | 524
Assets retired early [Member] |  |
Regulatory Assets [Line Items] |  |
Regulatory assets | 118 | 134
Asset retirement obligations [Member] |  |
Regulatory Assets [Line Items] |  |
Regulatory assets | 115 | 112
IPL's DAEC PPA amendment [Member] |  |
Regulatory Assets [Line Items] |  |
Regulatory assets | 110 | 108
Derivatives [Member] |  |
Regulatory Assets [Line Items] |  |
Regulatory assets | 20 | 39
Emission allowances [Member] |  |
Regulatory Assets [Line Items] |  |
Regulatory assets | 19 | 21
Other [Member] |  |
Regulatory Assets [Line Items] |  |
Regulatory assets | 85 | 89
IPL [Member] |  |
Regulatory Assets [Line Items] |  |
Regulatory assets | 1,418 | 1,400
IPL [Member] | Tax-related [Member] |  |
Regulatory Assets [Line Items] |  |
Regulatory assets | 829 | 777
IPL [Member] | Pension and OPEB costs [Member] |  |
Regulatory Assets [Line Items] |  |
Regulatory assets | 247 | 263
IPL [Member] | Assets retired early [Member] |  |
Regulatory Assets [Line Items] |  |
Regulatory assets | 79 | 88
IPL [Member] | Asset retirement obligations [Member] |  |
Regulatory Assets [Line Items] |  |
Regulatory assets | 79 | 76
IPL [Member] | IPL's DAEC PPA amendment [Member] |  |
Regulatory Assets [Line Items] |  |
Regulatory assets | 110 | 108
IPL [Member] | Derivatives [Member] |  |
Regulatory Assets [Line Items] |  |
Regulatory assets | 8 | 18
IPL [Member] | Emission allowances [Member] |  |
Regulatory Assets [Line Items] |  |
Regulatory assets | 19 | 21
IPL [Member] | Other [Member] |  |
Regulatory Assets [Line Items] |  |
Regulatory assets | 47 | 49
WPL [Member] |  |
Regulatory Assets [Line Items] |  |
Regulatory assets | 418 | 445
WPL [Member] | Tax-related [Member] |  |
Regulatory Assets [Line Items] |  |
Regulatory assets | 48 | 41
WPL [Member] | Pension and OPEB costs [Member] |  |
Regulatory Assets [Line Items] |  |
Regulatory assets | 245 | 261
WPL [Member] | Assets retired early [Member] |  |
Regulatory Assets [Line Items] |  |
Regulatory assets | 39 | 46
WPL [Member] | Asset retirement obligations [Member] |  |
Regulatory Assets [Line Items] |  |
Regulatory assets | 36 | 36
WPL [Member] | Derivatives [Member] |  |
Regulatory Assets [Line Items] |  |
Regulatory assets | 12 | 21
WPL [Member] | Other [Member] |  |
Regulatory Assets [Line Items] |  |
Regulatory assets | $ 38 | $ 40

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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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