Receivables (Receivables Sold Under The Agreement) (Details) - IPL [Member] - USD ($) $ in Millions		Jun. 30, 2015	Dec. 31, 2014
Receivables [Line Items]
Receivables sold to third party		$ 177.8
Receivables Sold [Member]
Receivables [Line Items]
Customer accounts receivable		100.4	$ 134.8
Unbilled utility revenues		77.2	69.7
Other receivables		0.2	0.1
Receivables sold to third party		177.8	204.6
Less: cash proceeds	[1]	100.0	22.0
Deferred proceeds		77.8	182.6
Less: allowance for doubtful accounts		4.4	5.4
Fair value of deferred proceeds		73.4	177.2
Outstanding receivables past due		$ 14.0	$ 19.9

[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.