Related Parties (Narrative) (Details) (USD $) In Millions	3 Months Ended	9 Months Ended
Jun. 30, 2011 IPL [Member] Franklin County Wind Project [Member]	Sep. 30, 2011 IPL [Member]	Sep. 30, 2010 IPL [Member]	Dec. 31, 2010 IPL [Member]	Sep. 30, 2011 WPL owed ATC [Member]	Dec. 31, 2010 WPL owed ATC [Member]
Net Amounts Owed		$ 75.1		$ 78.5	$ 6.3	$ 6.8
Proceeds from sale of wind project assets to affiliate	$ 115.3	$ 115.3

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 FASB

-Name Accounting Standards Codification

-Topic 850

-SubTopic 10

-Section 50

-Paragraph 1

-Subparagraph (d)

-URI http://asc.fasb.org/extlink&oid=6457730&loc=d3e39549-107864

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

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Article 4

-Section 08

-Paragraph k

-Subparagraph 1

Reference 3: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 57

-Paragraph 2

-Subparagraph d

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009.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 4: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 235

-SubTopic 10

-Section S99

-Paragraph 1

-Subparagraph (SX 210.4-08.(k)(1))

-URI http://asc.fasb.org/extlink&oid=6881521&loc=d3e23780-122690

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