Summary Of Significant Accounting Policies (Narrative) (Details) $ in Millions	12 Months Ended
	Dec. 31, 2025	Dec. 31, 2024 USD ($) customer MW	Dec. 31, 2023 USD ($)	Dec. 31, 2022
Cash, Cash Equivalents and Restricted Cash:
Money market fund investments		$ 52	$ 45
Money market fund investments interest rate, percentage		4.00%
Non-utility wind farm in Oklahoma [Member]
General:
Ownership interest		50.00%
IPL [Member]
General:
Generation and distribution of steam, number of customers served (in customers) | customer		2
Cash, Cash Equivalents and Restricted Cash:
Money market fund investments		$ 9	45
Money market fund investments interest rate, percentage		4.00%
Property, Plant and Equipment:
AFUDC accrual recorded, percentage of estimated CWIP		100.00%
WPL [Member]
Cash, Cash Equivalents and Restricted Cash:
Money market fund investments		$ 43	$ 0
Money market fund investments interest rate, percentage		4.00%
Property, Plant and Equipment:
AFUDC accrual recorded, percentage of estimated CWIP		50.00%
AFUDC accrual recorded, percentage earning a return as part of rate base		50.00%
AFUDC rates, projects with approval, percent		100.00%
Alliant Energy Finance, LLC [Member] | Non-utility wind farm in Oklahoma [Member]
General:
Ownership interest		50.00%
Electric capacity of wind farm (in megawatts) | MW		225
Sheboygan Falls Energy Facility [Member]
General:
Fossil-fueled EGU capacity (in megawatts) | MW		347
Electric - generation [Member] | IPL [Member]
Property, Plant and Equipment:
Average rate of depreciation, percent		3.30%	3.30%	3.40%
Electric - generation [Member] | WPL [Member]
Property, Plant and Equipment:
Average rate of depreciation, percent		3.40%	3.00%	3.40%
Electric - distribution [Member] | IPL [Member]
Property, Plant and Equipment:
Average rate of depreciation, percent		2.80%	2.80%	2.80%
Electric - distribution [Member] | WPL [Member]
Property, Plant and Equipment:
Average rate of depreciation, percent		2.70%	2.70%	2.50%
Forecast [Member] | Electric - generation [Member] | IPL [Member]
Property, Plant and Equipment:
Average rate of depreciation, percent	3.80%
Forecast [Member] | Electric - distribution [Member] | IPL [Member]
Property, Plant and Equipment:
Average rate of depreciation, percent	3.00%