Receivables (Narrative) (Details) - USD ($) $ in Millions		6 Months Ended
		Jun. 30, 2014	Jun. 30, 2015	Dec. 31, 2014
IPL [Member]
Receivables [Line Items]
Receivables sold to third party			$ 177.8
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			177.8	$ 204.6
Cash proceeds of receivables sold	[1]		100.0	22.0
Deferred proceeds			$ 73.4	$ 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.