Short-Term Debt (Narrative) (Details) (USD $) In Millions	Jun. 30, 2011	Dec. 31, 2010
Commercial paper outstanding		$ 47.4
Alliant Energy Corporation Parent [Member]
Commercial paper outstanding	0
IPL [Member]
Commercial paper outstanding	0
WPL [Member]
Commercial paper outstanding	$ 0	$ 47.4

Carrying value as of the balance sheet date of short-term borrowings using unsecured obligations issued by banks, corporations and other borrowers to investors. The maturities of these money market securities generally do not exceed 270 days.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher SEC
-Name Regulation S-X (SX)
-Number 210
-Section 03
-Paragraph 16
-Article 7

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher SEC
-Name Regulation S-X (SX)
-Number 210
-Section 02
-Paragraph 19
-Subparagraph a(3)
-Article 5

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher SEC
-Name Regulation S-X (SX)
-Number 210
-Section 03
-Paragraph 13
-Subparagraph 2
-Article 9

Name:	us-gaap_CommercialPaper
Namespace Prefix:	us-gaap
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant