Receivables (Narrative) (Details) (USD $) In Millions, unless otherwise specified	9 Months Ended			1 Months Ended
Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013 IPL [Member]	Dec. 31, 2012 IPL [Member]	Oct. 31, 2013 Senior Debentures [Member] 4.7% senior debentures [Domain] Subsequent Event [Member] IPL [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Receivables sold			$ 229.8	$ 198.4
Proceeds from issuance of long-term debt	0	75.0			250.0
Proceeds from Franklin County wind project cash grant	$ 62.4	$ 0

The cash inflow from a debt initially having maturity due after one year or beyond the operating cycle, if longer.

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

-Publisher FASB

-Name Accounting Standards Codification

-Glossary Financing Activities

-URI http://asc.fasb.org/extlink&oid=6513228

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

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 95

-Paragraph 18

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009.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 3: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 230

-SubTopic 10

-Section 45

-Paragraph 14

-Subparagraph (b)

-URI http://asc.fasb.org/extlink&oid=6943989&loc=d3e3255-108585

Reference 4: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 95

-Paragraph 19

-Subparagraph b

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009.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.

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