Receivables (Receivables Sold Under The Agreement) (Details) - USD ($) $ in Millions		Sep. 30, 2017	Dec. 31, 2016
Receivables [Line Items]
Fair value of deferred proceeds		$ 115.3	$ 211.1
IPL [Member]
Receivables [Line Items]
Fair value of deferred proceeds		115.3	211.1
Receivables Sold [Member] | IPL [Member]
Receivables [Line Items]
Customer accounts receivable		153.6	157.6
Unbilled utility revenues		89.1	90.4
Other receivables		1.1	0.1
Receivables sold to third party		243.8	248.1
Less: cash proceeds	[1]	112.0	21.0
Deferred proceeds		131.8	227.1
Less: allowance for doubtful accounts		16.5	16.0
Fair value of deferred proceeds		$ 115.3	$ 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.