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Debt (Other Short-Term Borrowings) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Debt Instrument [Line Items]
Maximum amount outstanding (based on daily outstanding balances)	$ 495	$ 601
Average amount outstanding (based on daily outstanding balances)	$ 292	$ 453
Weighted average interest rates	0.70%	2.50%
IPL [Member]
Debt Instrument [Line Items]
Maximum amount outstanding (based on daily outstanding balances)	$ 8	$ 50
Average amount outstanding (based on daily outstanding balances)	$ 0	$ 0
Weighted average interest rates	0.50%	2.80%
WPL [Member]
Debt Instrument [Line Items]
Maximum amount outstanding (based on daily outstanding balances)	$ 266	$ 195
Average amount outstanding (based on daily outstanding balances)	$ 117	$ 93
Weighted average interest rates	0.70%	2.40%

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- 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.

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- Definition

Weighted average interest rate of short-term debt outstanding calculated over time.

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- Definition

For the form of debt having an initial term of less than one year or less than the normal operating cycle, if longer, average borrowings during the period.

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- Definition

For the form of debt having an initial term of less than one year or less than the normal operating cycle, if longer, the maximum amount borrowed at any time during the period.

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