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Debt (Narrative) (Details) - USD ($) $ in Millions | Dec. 31, 2020 | Dec. 31, 2019
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Debt Instrument [Line Items] |  |
Line of credit facility, current borrowing capacity |  | $ 1,000
Non-recourse debt and hybrid securities consolidated capital maximum limit |  | 15.00%
Parent Company [Member] |  |
Debt Instrument [Line Items] |  |
Line of credit facility, current borrowing capacity |  | $ 450
IPL [Member] |  |
Debt Instrument [Line Items] |  |
Line of credit facility, current borrowing capacity |  | 250
WPL [Member] |  |
Debt Instrument [Line Items] |  |
Line of credit facility, current borrowing capacity |  | $ 300
Forecast [Member] | Parent Company [Member] |  |
Debt Instrument [Line Items] |  |
Line of credit facility, maximum borrowing capacity | $ 500 |
Forecast [Member] | IPL [Member] |  |
Debt Instrument [Line Items] |  |
Line of credit facility, maximum borrowing capacity | 400 |
Forecast [Member] | WPL [Member] |  |
Debt Instrument [Line Items] |  |
Line of credit facility, maximum borrowing capacity | $ 500 |

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- Definition Amount of current borrowing capacity under the credit facility considering any current restrictions on the amount that could be borrowed (for example, borrowings may be limited by the amount of current assets), but without considering any amounts currently outstanding under the facility. + 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 210.5-02.19(b),22(b)) -URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682 + Details
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- Definition Maximum borrowing capacity under the credit facility without consideration of any current restrictions on the amount that could be borrowed or the amounts currently outstanding under the facility. + 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 210.5-02.19(b),22(b)) -URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682 + Details
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