Derivative Instruments (Fair Value Of Financial Instruments) (Details) (Commodity Contracts [Member], USD $) In Millions, unless otherwise specified	Mar. 31, 2015	Dec. 31, 2014
Derivatives, Fair Value [Line Items]
Current derivative assets	$ 9.1us-gaap_DerivativeAssetsCurrent	$ 30.5us-gaap_DerivativeAssetsCurrent
Non-current derivative assets	7.8us-gaap_DerivativeAssetsNoncurrent	8.1us-gaap_DerivativeAssetsNoncurrent
Current derivative liabilities	24.4us-gaap_DerivativeLiabilitiesCurrent	28.1us-gaap_DerivativeLiabilitiesCurrent
Non-current derivative liabilities	18.3us-gaap_DerivativeLiabilitiesNoncurrent	9.5us-gaap_DerivativeLiabilitiesNoncurrent
IPL [Member]
Derivatives, Fair Value [Line Items]
Current derivative assets	5.6	27.4
Non-current derivative assets	0.9	0.6
Current derivative liabilities	13.8	16.4
Non-current derivative liabilities	6.2	3.1
WPL [Member]
Derivatives, Fair Value [Line Items]
Current derivative assets	3.5	3.1
Non-current derivative assets	6.9	7.5
Current derivative liabilities	10.6	11.7
Non-current derivative liabilities	$ 12.1	$ 6.4

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