v2.4.0.6

Derivative Instruments (Fair Value Of Financial Instruments) (Details) (USD $) In Millions, unless otherwise specified	Dec. 31, 2012	Dec. 31, 2011
Derivatives, Fair Value [Line Items]
Current derivative liabilities	$ 31.1	$ 55.9
IPL [Member]
Derivatives, Fair Value [Line Items]
Current derivative liabilities	14.1	24.5
WPL [Member]
Derivatives, Fair Value [Line Items]
Current derivative liabilities	17.0	31.4
Commodity Contracts [Member]
Derivatives, Fair Value [Line Items]
Current derivative assets	23.5	12.7
Non-current derivative assets	2.7	3.0
Current derivative liabilities	31.1	55.9
Non-current derivative liabilities	9.3	22.1
Commodity Contracts [Member] | IPL [Member]
Derivatives, Fair Value [Line Items]
Current derivative assets	17.0	9.2
Non-current derivative assets	0.5	1.4
Current derivative liabilities	14.1	24.5
Non-current derivative liabilities	2.0	9.1
Commodity Contracts [Member] | WPL [Member]
Derivatives, Fair Value [Line Items]
Current derivative assets	6.5	3.5
Non-current derivative assets	2.2	1.6
Current derivative liabilities	17.0	31.4
Non-current derivative liabilities	$ 7.3	$ 13.0

X

- Definition

Fair values as of the balance sheet date for all assets resulting from contracts that meet the criteria of being accounted for as derivative instruments and which are expected to be converted into cash or otherwise disposed of within a year or the normal operating cycle, if longer, net of the effects of master netting arrangements.

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