Receivables (Receivables Sold Under The Agreement) (Details) - Receivables Sold [Member] - IPL [Member] - USD ($) $ in Millions		Mar. 31, 2016	Dec. 31, 2015
Receivables [Line Items]
Customer accounts receivable		$ 142.7	$ 109.7
Unbilled utility revenues		77.5	71.3
Other receivables		0.3	0.1
Receivables sold to third party		220.5	181.1
Less: cash proceeds	[1]	62.0	5.0
Deferred proceeds		158.5	176.1
Less: allowance for doubtful accounts		4.3	4.1
Fair value of deferred proceeds		$ 154.2	$ 172.0

[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.