Debt (Narrative) (Details) - USD ($)	1 Months Ended
	Jun. 30, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Debt Instrument [Line Items]
Line of credit facility, current borrowing capacity			$ 1,000,000,000
Non-recourse debt and hybrid securities consolidated capital maximum limit			15.00%
Parent Company [Member]
Debt Instrument [Line Items]
Line of credit facility, current borrowing capacity			$ 400,000,000
IPL [Member]
Debt Instrument [Line Items]
Line of credit facility, current borrowing capacity			250,000,000
WPL [Member]
Debt Instrument [Line Items]
Line of credit facility, current borrowing capacity			$ 350,000,000
Scenario, Forecast [Member] | Parent Company [Member]
Debt Instrument [Line Items]
Line of credit facility, maximum borrowing capacity		$ 500,000,000
Scenario, Forecast [Member] | IPL [Member]
Debt Instrument [Line Items]
Line of credit facility, maximum borrowing capacity		400,000,000
Scenario, Forecast [Member] | WPL [Member]
Debt Instrument [Line Items]
Line of credit facility, maximum borrowing capacity		$ 500,000,000
Term Loan Credit Agreement [Member] | Alliant Energy Finance, LLC [Member]
Debt Instrument [Line Items]
Repayments of debt	$ 95,000,000
Variable-rate term loan credit agreement, period	364 days
Interest rate				2.20%