Receivables (Receivables Sold Under The Agreement) (Details) (USD $) In Millions, unless otherwise specified	Sep. 30, 2014		Dec. 31, 2013
Receivables [Line Items]
Fair value of deferred proceeds	$ 160.3		$ 203.5
IPL [Member]
Receivables [Line Items]
Customer accounts receivable	142.6		151.6
Unbilled utility revenues	60.7		86.2
Other receivables	0.4		0.2
Receivables sold	203.7		238.0
Less: cash proceeds	38.0	[1]	29.0	[1]
Deferred proceeds	165.7		209.0
Less: allowance for doubtful accounts	5.4		5.5
Fair value of deferred proceeds	160.3		203.5
Outstanding receivables past due	$ 17.8		$ 21.5

[1] Changes in cash proceeds are presented in “Accounts receivable” in operating activities in Alliant Energy’s and IPL’s cash flows statements.