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Property, Plant and Equipment (Equity and Debt AFUDC) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Property, Plant and Equipment [Line Items]
Allowance for funds used during construction	$ 55	$ 93	$ 76
Equity [Member]
Property, Plant and Equipment [Line Items]
Allowance for funds used during construction	39	66	51
Debt [Member]
Property, Plant and Equipment [Line Items]
Allowance for funds used during construction	16	27	25
IPL [Member]
Property, Plant and Equipment [Line Items]
Allowance for funds used during construction	24	50	42
IPL [Member] | Equity [Member]
Property, Plant and Equipment [Line Items]
Allowance for funds used during construction	17	35	29
IPL [Member] | Debt [Member]
Property, Plant and Equipment [Line Items]
Allowance for funds used during construction	7	15	13
WPL [Member]
Property, Plant and Equipment [Line Items]
Allowance for funds used during construction	31	43	34
WPL [Member] | Equity [Member]
Property, Plant and Equipment [Line Items]
Allowance for funds used during construction	22	31	22
WPL [Member] | Debt [Member]
Property, Plant and Equipment [Line Items]
Allowance for funds used during construction	$ 9	$ 12	$ 12

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+ References

No definition available.

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Total increase in earnings in the period representing the cost of equity (based on assumed rate of return) and/or borrowed funds (based on interest rate) used to finance construction of regulated assets, which is expected to be recovered through rate adjustments.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 28
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=121586364&loc=d3e3602-108585

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 980
-SubTopic 340
-Section 50
-Paragraph 3
-URI http://asc.fasb.org/extlink&oid=6499975&loc=d3e44278-110382

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-Publisher FASB
-Name Accounting Standards Codification
-Topic 980
-SubTopic 360
-Section 25
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=6500269&loc=d3e45485-110386

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