Receivables (Narrative) (Details) - USD ($) $ in Millions		Sep. 30, 2016	Dec. 31, 2015
Receivables [Line Items]
Deferred proceeds		$ 239.7	$ 172.0
IPL [Member]
Receivables [Line Items]
Deferred proceeds		239.7	172.0
Receivables Sold [Member] | IPL [Member]
Receivables [Line Items]
Receivables sold to third party		252.9	181.1
Cash proceeds of receivables sold	[1]	1.0	5.0
Deferred proceeds		239.7	$ 172.0
Outstanding receivables past due		$ 64.5

[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.