Summary Of Significant Accounting Policies (Narrative) (Details) $ in Millions	12 Months Ended
	Dec. 31, 2018 USD ($) customer MW	Dec. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)	Jan. 01, 2019 USD ($)
New Accounting Standards:
Adjustment To Net Periodic Benefit Costs, Percentage	40.00%
Income statement impact of adopting new pension and other postretirement plans accounting standard		$ 17.8	$ 17.1
Cash receipts on sold receivables	$ 605.3	461.8	466.8
IPL [Member]
General:
Generation and distribution of steam, number of customers served (in customers) | customer	2
Property, Plant and Equipment:
AFUDC accrual recorded, percentage of estimated CWIP	100.00%
New Accounting Standards:
Income statement impact of adopting new pension and other postretirement plans accounting standard		7.2	6.8
Cash receipts on sold receivables	$ 605.3	461.8	466.8
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:
Income statement impact of adopting new pension and other postretirement plans accounting standard		10.5	10.2
Alliant Energy Finance, LLC [Member]
General:
Ownership interest	50.00%
Electric capacity of wind farm (in megawatts) | MW	225
Alliant Energy and IPL [Member]
New Accounting Standards:
Cash receipts on sold receivables		$ 461.8	$ 466.8
Sheboygan Falls Energy Facility [Member]
General:
Fossil-fueled EGU capacity (in megawatts) | MW	347
Capital lease, lease term	20 years
Scenario, Forecast [Member]
New Accounting Standards:
Balance sheet impact of adopting new lease accounting standard				$ 18.0
Scenario, Forecast [Member] | IPL [Member]
New Accounting Standards:
Balance sheet impact of adopting new lease accounting standard				11.0
Scenario, Forecast [Member] | WPL [Member]
New Accounting Standards:
Balance sheet impact of adopting new lease accounting standard				$ 7.0