Receivables (Narrative) (Details) - USD ($) $ in Millions		Mar. 31, 2017	Dec. 31, 2016
Receivables [Line Items]
Deferred proceeds		$ 149.0	$ 211.1
IPL [Member]
Receivables [Line Items]
Deferred proceeds		149.0	211.1
Receivables Sold [Member] | IPL [Member]
Receivables [Line Items]
Receivables sold to third party		221.0	248.1
Cash proceeds of receivables sold	[1]	56.0	21.0
Deferred proceeds		149.0	$ 211.1
Available capacity		41.8
Outstanding receivables past due		$ 69.9

[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.