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Regulatory Matters (Regulatory Liabilities) (Details) (USD $) In Millions, unless otherwise specified	Mar. 31, 2014	Dec. 31, 2013
Regulatory Liabilities [Line Items]
Regulatory liabilities	$ 836.4	$ 821.5
Cost of removal obligations [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	420.0	418.9
IPL's tax benefit riders [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	239.8	265.4
Energy efficiency cost recovery [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	64.1	52.7
Derivatives [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	33.3	7.2
IPL's electric transmission cost recovery [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	21.2	14.6
IPL's electric transmission assets sale [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	18.8	21.6
Other [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	39.2	41.1
IPL [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	604.0	614.9
IPL [Member] | Cost of removal obligations [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	279.3	277.7
IPL [Member] | IPL's tax benefit riders [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	239.8	265.4
IPL [Member] | Energy efficiency cost recovery [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	14.9	9.3
IPL [Member] | Derivatives [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	8.8	3.6
IPL [Member] | IPL's electric transmission cost recovery [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	21.2	14.6
IPL [Member] | IPL's electric transmission assets sale [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	18.8	21.6
IPL [Member] | Other [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	21.2	22.7
WPL [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	232.4	206.6
WPL [Member] | Cost of removal obligations [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	140.7	141.2
WPL [Member] | Energy efficiency cost recovery [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	49.2	43.4
WPL [Member] | Derivatives [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	24.5	3.6
WPL [Member] | Other [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	$ 18.0	$ 18.4

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- Definition

The amount for the individual regulatory liability as itemized in a table of regulatory liabilities as of the end of the period.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 980

-SubTopic 405

-Section 25

-Paragraph 1

-URI http://asc.fasb.org/extlink&oid=6500807&loc=d3e48068-110394

+ Details

Name:	us-gaap_RegulatoryLiabilities
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

X

- Details

Name:	us-gaap_RegulatoryLiabilitiesLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration