Receivables (Receivables Sold Under The Agreement) (Details) - USD ($) $ in Millions		Mar. 31, 2017	Dec. 31, 2016
Receivables [Line Items]
Fair value of deferred proceeds		$ 149.0	$ 211.1
IPL [Member]
Receivables [Line Items]
Fair value of deferred proceeds		149.0	211.1
Receivables Sold [Member] | IPL [Member]
Receivables [Line Items]
Customer accounts receivable		143.7	157.6
Unbilled utility revenues		76.8	90.4
Other receivables		0.5	0.1
Receivables sold to third party		221.0	248.1
Less: cash proceeds	[1]	56.0	21.0
Deferred proceeds		165.0	227.1
Less: allowance for doubtful accounts		16.0	16.0
Fair value of deferred proceeds		$ 149.0	$ 211.1

[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.