Receivables (Narrative) (Details) - USD ($) $ in Millions		9 Months Ended
		Sep. 30, 2014	Sep. 30, 2015	Dec. 31, 2014
Whiting Petroleum Corporation [Member]
Receivables [Line Items]
Final payment of certain future tax benefits expected to be realized		$ 26.0
Receivables Sold [Member] | IPL [Member]
Receivables [Line Items]
Receivables sold to third party			$ 201.2	$ 204.6
Cash proceeds of receivables sold	[1]		1.0	22.0
Deferred proceeds			$ 195.5	$ 177.2

[1] Changes in cash proceeds are presented in “Sales of accounts receivable” in operating activities in Alliant Energy’s and IPL’s cash flows statements.