v2.4.0.6

Benefit Plans (Employees Participate In Defined Contribution Retirement Plans) (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended				9 Months Ended
	Sep. 30, 2012		Sep. 30, 2011		Sep. 30, 2012		Sep. 30, 2011
Alliant Energy [Member]
401(k) costs	$ 4.4		$ 4.4		$ 14.1		$ 14.3
IPL [Member]
401(k) costs	2.4	[1]	2.2	[1]	7.4	[1]	7.1	[1]
WPL [Member]
401(k) costs	$ 2.0	[1]	$ 2.0	[1]	$ 6.2	[1]	$ 6.6	[1]
[1] IPL’s and WPL’s amounts include allocated costs associated with Corporate Services employees.

X

- Definition

The amount of the cost recognized during the period for defined contribution plans.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 132R

-Paragraph 11

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.



Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 715

-SubTopic 70

-Section 50

-Paragraph 1

-URI http://asc.fasb.org/extlink&oid=6414718&loc=d3e28014-114942

+ Details

Name:	us-gaap_DefinedContributionPlanCostRecognized
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration