Receivables (Narrative) (Details) - Receivables Sold [Member] - IPL [Member] - USD ($) $ in Millions		Mar. 31, 2016	Dec. 31, 2015
Receivables [Line Items]
Receivables sold to third party		$ 220.5	$ 181.1
Cash proceeds of receivables sold	[1]	62.0	5.0
Deferred proceeds		154.2	$ 172.0
Outstanding receivables past due		$ 47.5

[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.