Summary Of Significant Accounting Policies (Narrative) (Details) - USD ($) $ in Millions	3 Months Ended	6 Months Ended		12 Months Ended
	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017	Dec. 31, 2017
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Adjustment to net periodic benefit costs, percentage			40.00%
Income statement impact of adoption of Accounting Standards Update 2017-17	$ 4.4		$ 8.7
Cash receipts on sold receivables		$ 571.9	$ 374.5
IPL [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Adjustment to net periodic benefit costs, percentage			40.00%
Income statement impact of adoption of Accounting Standards Update 2017-17	1.8		$ 3.5
Cash receipts on sold receivables		$ 571.9	$ 374.5
WPL [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Adjustment to net periodic benefit costs, percentage			40.00%
Income statement impact of adoption of Accounting Standards Update 2017-17	$ 2.5		$ 5.1
Alliant Energy and IPL [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Cash receipts on sold receivables			$ 374.5	$ 681.9