Receivables (Receivables Sold Under The Agreement) (Details) - Receivables Sold [Member] - IPL [Member] - USD ($) $ in Millions		Jun. 30, 2016	Dec. 31, 2015
Receivables [Line Items]
Customer accounts receivable		$ 127.6	$ 109.7
Unbilled utility revenues		92.1	71.3
Other receivables		0.5	0.1
Receivables sold to third party		220.2	181.1
Less: cash proceeds	[1]	138.0	5.0
Deferred proceeds		82.2	176.1
Less: allowance for doubtful accounts		7.8	4.1
Fair value of deferred proceeds		$ 74.4	$ 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.