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Long-term Contract for Purchase of Electric Power, Buyout Payment

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Number Of Customers Without Power Derecho Windstorm

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Regulatory Matters [Line Items]

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Amount of regulatory costs not yet approved by the regulatory authority.

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Carrying amount as of the balance sheet date of capitalized storm costs of a regulated entity that are expected to be recoverable through rate adjustments after one year or beyond the normal operating cycle, if longer.

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Amount of public utility's approved rate increase (decrease) by regulatory agency.

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Percentage of public utility's approved rate increase (decrease) by regulatory agency.

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Amount of public utility's interim rate increase (decrease) allowed while waiting final decision of regulatory agency.

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The amount for the individual regulatory liability as itemized in a table of regulatory liabilities as of the end of the period.

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Regulatory Matters (Narrative) (Details) $ in Millions	1 Months Ended		12 Months Ended
Regulatory Matters (Narrative) (Details) $ in Millions	Sep. 30, 2020 USD ($)	Aug. 31, 2020 customer	Dec. 31, 2020 USD ($) MW	Dec. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)	Dec. 31, 2021 USD ($)
Regulatory Matters [Line Items]
Credits issued to customers			$ (113)	$ (40)	$ 1
Regulatory liabilities			1,306	1,424
Electric transmission cost recovery [Member]
Regulatory Matters [Line Items]
Regulatory liabilities			68	88
IPL [Member]
Regulatory Matters [Line Items]
Regulatory assets not earning a return			81
Credits issued to customers			$ (20)	2	1
Electric capacity of wind farm (in megawatts) \| MW			1,000
Regulatory liabilities			$ 676	715
IPL [Member] \| Electric transmission cost recovery [Member]
Regulatory Matters [Line Items]
Credits issued to customers			42
Regulatory liabilities			39	51
IPL [Member] \| Derecho windstorm [Member]
Regulatory Matters [Line Items]
Number of customers without power, derecho windstorm (number of customers) \| customer		250,000
Derecho windstorm repair and rebuilding costs			135
Net regulatory liability, derecho windstorm			7
WPL [Member]
Regulatory Matters [Line Items]
Regulatory assets not earning a return			11
Credits issued to customers			(93)	(42)	1
Regulatory liabilities			630	709
WPL [Member] \| Electric transmission cost recovery [Member]
Regulatory Matters [Line Items]
Regulatory liabilities			29	37
2020 Test Period Retail Electric [Member] \| IPL [Member]
Regulatory Matters [Line Items]
Interim rate increase (decrease), amount				$ 90
Authorized increase (decrease) in final rates, amount			127
2020 Test Period Retail Electric [Member] \| IPL [Member] \| Tax-related [Member]
Regulatory Matters [Line Items]
Regulatory liabilities			27
2020 Test Period Retail Electric [Member] \| IPL [Member] \| Revenue Subject to Refund [Member]
Regulatory Matters [Line Items]
Regulatory liabilities			8
2020 Test Period Retail Electric [Member] \| WPL [Member]
Regulatory Matters [Line Items]
Authorized increase (decrease) in final rates, amount			$ 29
Authorized increase (decrease) in final rates, percentage			2.00%
2020 Test Period Retail Gas [Member] \| IPL [Member]
Regulatory Matters [Line Items]
Authorized increase (decrease) in final rates, amount			$ 12
2016 Test Year Retail Electric [Member] \| IPL [Member]
Regulatory Matters [Line Items]
Interim rate increase (decrease), amount						$ 102
Authorized increase (decrease) in final rates, amount					$ 130
2019 Test Period Retail Electric [Member] \| WPL [Member] \| Revenue Subject to Refund [Member]
Regulatory Matters [Line Items]
Credits issued to customers			$ 12
DAEC PPA [Member]
Regulatory Matters [Line Items]
Buyout payment	$ 110
PPA term amendment			5 years
Forecast [Member] \| IPL [Member] \| Derecho windstorm [Member]
Regulatory Matters [Line Items]
Derecho windstorm repair and rebuilding costs							$ 140