Derivative Instruments (Fair Value Of Financial Instruments) (Details) (Commodity Contracts [Member], USD $) In Millions, unless otherwise specified	Mar. 31, 2014	Dec. 31, 2013
Derivatives, Fair Value [Line Items]
Current derivative assets	$ 31.5	$ 25.6
Non-current derivative assets	9.8	1.1
Current derivative liabilities	4.2	6.7
Non-current derivative liabilities	4.8	14.1
IPL [Member]
Derivatives, Fair Value [Line Items]
Current derivative assets	15.4	20.2
Non-current derivative assets	0.5	0.9
Current derivative liabilities	1.1	3.0
Non-current derivative liabilities	1.1	2.2
WPL [Member]
Derivatives, Fair Value [Line Items]
Current derivative assets	16.1	5.4
Non-current derivative assets	9.3	0.2
Current derivative liabilities	3.1	3.7
Non-current derivative liabilities	$ 3.7	$ 11.9

Fair value, after the effects of master netting arrangements, of a financial asset or other contract with one or more underlyings, notional amount or payment provision or both, and the contract can be net settled by means outside the contract or delivery of an asset, expected to be settled within one year or normal operating cycle, if longer. Includes assets not subject to a master netting arrangement and not elected to be offset.

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Fair value, after the effects of master netting arrangements, of a financial asset or other contract with one or more underlyings, notional amount or payment provision or both, and the contract can be net settled by means outside the contract or delivery of an asset, expected to be settled after one year or the normal operating cycle, if longer. Includes assets not subject to a master netting arrangement and not elected to be offset.

+ References+ Details

- Definition

Fair value, after the effects of master netting arrangements, of a financial liability or contract with one or more underlyings, notional amount or payment provision or both, and the contract can be net settled by means outside the contract or delivery of an asset, expected to be settled within one year or normal operating cycle, if longer. Includes assets not subject to a master netting arrangement and not elected to be offset.

+ References+ Details

- Definition

Fair value, after the effects of master netting arrangements, of a financial liability or contract with one or more underlyings, notional amount or payment provision or both, and the contract can be net settled by means outside the contract or delivery of an asset, expected to be settled after one year or the normal operating cycle, if longer. Includes assets not subject to a master netting arrangement and not elected to be offset.

+ References+ Details