Derivative Instruments (Fair Value Of Financial Instruments) (Details) - Commodity Contracts [Member] - USD ($) $ in Millions	Sep. 30, 2019	Dec. 31, 2018
Derivatives, Fair Value [Line Items]
Current derivative assets	$ 18.6	$ 24.6
Non-current derivative assets	11.7	3.7
Current derivative liabilities	13.4	5.6
Non-current derivative liabilities	18.4	17.7
IPL [Member]
Derivatives, Fair Value [Line Items]
Current derivative assets	12.8	16.1
Non-current derivative assets	10.5	1.6
Current derivative liabilities	5.6	3.1
Non-current derivative liabilities	7.8	8.1
WPL [Member]
Derivatives, Fair Value [Line Items]
Current derivative assets	5.8	8.5
Non-current derivative assets	1.2	2.1
Current derivative liabilities	7.8	2.5
Non-current derivative liabilities	$ 10.6	$ 9.6

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.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 20
-Section 50
-Paragraph 3
-Subparagraph (c)
-URI http://asc.fasb.org/extlink&oid=51824906&loc=SL20225862-175312

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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.

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- Definition

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