Receivables (Receivables Sold Under The Agreement) (Details) - Receivables Sold [Member] - IPL [Member] - USD ($) $ in Millions		Sep. 30, 2015	Dec. 31, 2014
Receivables [Line Items]
Customer accounts receivable		$ 128.1	$ 134.8
Unbilled utility revenues		72.8	69.7
Other receivables		0.3	0.1
Receivables sold to third party		201.2	204.6
Less: cash proceeds	[1]	1.0	22.0
Deferred proceeds		200.2	182.6
Less: allowance for doubtful accounts		4.7	5.4
Fair value of deferred proceeds		195.5	177.2
Outstanding receivables past due		$ 15.4	$ 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.