Summary Of Significant Accounting Policies (Narrative) (Details) $ in Millions	12 Months Ended
	Dec. 31, 2020 USD ($) customer MW	Dec. 31, 2019 USD ($)
Cash, Cash Equivalents and Restricted Cash [Abstract]
Money market fund investments	$ 44	$ 5
Money market fund investments interest rate, percentage	0.04%
New Accounting Standards:
New accounting standard, cumulative effect adjustment to retained earnings, after-tax	$ (2,994)	(2,766)
Cumulative Effect, Period of Adoption, Adjustment [Member]
New Accounting Standards:
New accounting standard, cumulative effect adjustment to retained earnings, pre-tax		12
New accounting standard, cumulative effect adjustment to retained earnings, after-tax		9
IPL [Member]
General:
Generation and distribution of steam, number of customers served (in customers) | customer	2
Electric capacity of wind farm (in megawatts) | MW	1,000
Cash, Cash Equivalents and Restricted Cash [Abstract]
Money market fund investments	$ 44	5
Money market fund investments interest rate, percentage	0.04%
Property, Plant and Equipment:
AFUDC accrual recorded, percentage of estimated CWIP	100.00%
New Accounting Standards:
New accounting standard, cumulative effect adjustment to retained earnings, after-tax	$ (979)	(891)
WPL [Member]
Property, Plant and Equipment:
AFUDC accrual recorded, percentage of estimated CWIP	50.00%
AFUDC rates, projects with approval	100.00%
New Accounting Standards:
New accounting standard, cumulative effect adjustment to retained earnings, after-tax	$ (953)	$ (864)
Alliant Energy Finance, LLC [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
Finance lease, lease term	20 years