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Fair Value Measurements (Fair Value Of Net Derivative Assets (Liabilities)) (Details) - Commodity Contracts [Member] - USD ($) $ in Millions	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair value, net derivative assets	$ 29	$ 21	$ 12
Excluding FTRs [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair value, net derivative assets	18	15
FTRs [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair value, net derivative assets	11	7
IPL [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair value, net derivative assets	26	18	$ 9
IPL [Member] | Excluding FTRs [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair value, net derivative assets	17	14
IPL [Member] | FTRs [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair value, net derivative assets	9	5
WPL [Member] | Excluding FTRs [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair value, net derivative assets	1	1
WPL [Member] | FTRs [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair value, net derivative assets	$ 2	$ 2

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- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

No definition available.

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- Definition

Fair value of financial instrument classified as an asset measured using unobservable inputs that reflect the entity's own assumption about the assumptions market participants would use in pricing.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 820
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (c)
-URI http://asc.fasb.org/extlink&oid=117815213&loc=d3e19207-110258

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