Derivative Instruments (Narrative) (Details) (USD $) In Millions, unless otherwise specified	Sep. 30, 2014
Derivative Instruments [Line Items]
Cash collateral posted by counterparties	$ 4.7
IPL [Member]
Derivative Instruments [Line Items]
Cash collateral posted by counterparties	0.3
WPL [Member]
Derivative Instruments [Line Items]
Cash collateral posted by counterparties	$ 4.4

The aggregate fair value of assets that are already posted, at the end of the reporting period, as collateral for derivative instruments with credit-risk-related contingent features.

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 815

-SubTopic 10

-Section 50

-Paragraph 4H

-Subparagraph (d)

-URI http://asc.fasb.org/extlink&oid=35706170&loc=SL5624258-113959

Name:	us-gaap_CollateralAlreadyPostedAggregateFairValue
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant