Receivables (Receivables Sold Under The Agreement) (Details) (USD $) In Millions, unless otherwise specified	Jun. 30, 2014		Dec. 31, 2013
Accounts, Notes, Loans and Financing Receivable [Line Items]
Fair value of deferred proceeds	$ 193.7		$ 203.5
IPL [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Customer accounts receivable	136.0		151.6
Unbilled utility revenues	73.2		86.2
Other receivables	0.1		0.2
Receivables sold	209.3		238.0
Less: cash proceeds	10.0	[1]	29.0	[1]
Deferred proceeds	199.3		209.0
Less: allowance for doubtful accounts	5.6		5.5
Fair value of deferred proceeds	193.7		203.5
Outstanding receivables past due	$ 18.8		$ 21.5

[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.