Debt (Narrative) (Details) - USD ($)	1 Months Ended	3 Months Ended
	Apr. 30, 2019	Mar. 31, 2019
Debt [Line Items]
Credit facility agreement, extension		1 year
Line of credit facility, current borrowing capacity		$ 1,000,000,000
IPL [Member]
Debt [Line Items]
Line of credit facility, current borrowing capacity		250,000,000
WPL [Member]
Debt [Line Items]
Line of credit facility, current borrowing capacity		300,000,000
Alliant Energy and IPL [Member]
Debt [Line Items]
Commercial paper, long-term		$ 115,000,000
Commercial paper, long-term, interest rate percent		2.70%
Senior Debentures [Member] | Subsequent Event [Member] | 3.6% senior debentures due 2029 [Member] | IPL [Member]
Debt [Line Items]
Proceeds from issuance of long-term debt	$ 300,000,000
Interest rate, percent	3.60%
Parent Company [Member]
Debt [Line Items]
Line of credit facility, current borrowing capacity		$ 450,000,000