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Summary Of Significant Accounting Policies (Regulatory Assets) (Details) (USD $) In Millions, unless otherwise specified	Sep. 30, 2013	Dec. 31, 2012
Regulatory Assets [Line Items]
Regulatory assets	$ 1,596.2	$ 1,612.4
Tax-related [Member]
Regulatory Assets [Line Items]
Regulatory assets	813.6	770.7
Pension and other postretirement benefits costs [Member]
Regulatory Assets [Line Items]
Regulatory assets	525.2	549.2
AROs [Member]
Regulatory Assets [Line Items]
Regulatory assets	66.9	62.4
Emission allowances [Member]
Regulatory Assets [Line Items]
Regulatory assets	30.0	30.0
Derivatives [Member]
Regulatory Assets [Line Items]
Regulatory assets	26.8	40.2
Environmental-related costs [Member]
Regulatory Assets [Line Items]
Regulatory assets	26.0	34.9
Other [Member]
Regulatory Assets [Line Items]
Regulatory assets	107.7	125.0
IPL [Member]
Regulatory Assets [Line Items]
Regulatory assets	1,216.0	1,217.9
IPL [Member] | Tax-related [Member]
Regulatory Assets [Line Items]
Regulatory assets	783.6	746.2
IPL [Member] | Pension and other postretirement benefits costs [Member]
Regulatory Assets [Line Items]
Regulatory assets	267.9	279.3
IPL [Member] | AROs [Member]
Regulatory Assets [Line Items]
Regulatory assets	38.8	38.6
IPL [Member] | Emission allowances [Member]
Regulatory Assets [Line Items]
Regulatory assets	30.0	30.0
IPL [Member] | Derivatives [Member]
Regulatory Assets [Line Items]
Regulatory assets	6.9	16.3
IPL [Member] | Environmental-related costs [Member]
Regulatory Assets [Line Items]
Regulatory assets	21.8	30.3
IPL [Member] | Other [Member]
Regulatory Assets [Line Items]
Regulatory assets	67.0	77.2
WPL [Member]
Regulatory Assets [Line Items]
Regulatory assets	380.2	394.5
WPL [Member] | Tax-related [Member]
Regulatory Assets [Line Items]
Regulatory assets	30.0	24.5
WPL [Member] | Pension and other postretirement benefits costs [Member]
Regulatory Assets [Line Items]
Regulatory assets	257.3	269.9
WPL [Member] | AROs [Member]
Regulatory Assets [Line Items]
Regulatory assets	28.1	23.8
WPL [Member] | Emission allowances [Member]
Regulatory Assets [Line Items]
Regulatory assets	0	0
WPL [Member] | Derivatives [Member]
Regulatory Assets [Line Items]
Regulatory assets	19.9	23.9
WPL [Member] | Environmental-related costs [Member]
Regulatory Assets [Line Items]
Regulatory assets	4.2	4.6
WPL [Member] | Other [Member]
Regulatory Assets [Line Items]
Regulatory assets	$ 40.7	$ 47.8

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X

- Definition

The amount for the individual regulatory asset as itemized in a table of regulatory assets as of the end of the period.

+ References

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

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 71

-Paragraph 9, 10

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 980

-SubTopic 340

-Section 50

-Paragraph 1

-URI http://asc.fasb.org/extlink&oid=6499975&loc=d3e44250-110382

+ Details

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