Related Parties (Net Intercompany Payables) (Details) (USD $) In Millions	Jun. 30, 2011	Dec. 31, 2010
IPL [Member]
Net Intercompany Payables	$ 86.5	$ 78.5
WPL [Member]
Net Intercompany Payables	$ 40.8	$ 41.6

Receivables to be collected from (obligations owed to) related parties, net as of the balance sheet date where one party can exercise control or significant influence over another party; including affiliates, owners or officers and their immediate families, pension trusts, and so forth.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher SEC
-Name Regulation S-X (SX)
-Number 210
-Section 08
-Paragraph k
-Subparagraph 1
-Article 4

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Statement of Financial Accounting Standard (FAS)
-Number 57
-Paragraph 2
-Subparagraph d

Name:	us-gaap_RelatedPartyTransactionDueFromToRelatedParty
Namespace Prefix:	us-gaap
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant