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- Definition

Reduction In Fuel-related Costs

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- Definition

Regulatory Matters [Line Items]

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- Definition

Amount of write-down of assets recognized in the income statement. Includes, but is not limited to, losses from tangible assets, intangible assets and goodwill.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 360
-SubTopic 10
-Section 45
-Paragraph 4
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-Section 45
-Paragraph 28
-Subparagraph (b)
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- Definition

Amount of cash outflow to customers for refund payments of revenue that was previously reported as deferred or unearned revenue.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 605
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SAB TOPIC 13.A.4(a).Q1 Response))
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- Definition

The current period expense charged against earnings on long-lived, physical assets not used in production, and which are not intended for resale, to allocate or recognize the cost of such assets over their useful lives; or to record the reduction in book value of an intangible asset over the benefit period of such asset; or to reflect consumption during the period of an asset that is not used in production.

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-Publisher FASB
-Name Accounting Standards Codification
-Topic 360
-SubTopic 10
-Section 50
-Paragraph 1
-Subparagraph (a)
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- Definition

Amount of public utility's approved rate increase (decrease) by regulatory agency.

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Percentage of public utility's approved rate increase (decrease) by regulatory agency.

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Amount of public utility's interim rate increase (decrease) allowed while waiting final decision of regulatory agency.

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Percentage of public utility's interim rate increase (decrease) allowed while waiting final decision of regulatory agency.

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- Definition

Amortization period for the recovery of regulatory asset, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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- Definition

The amount for the individual regulatory liability as itemized in a table of regulatory liabilities as of the end of the period.

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Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 980
-SubTopic 405
-Section 25
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=6500807&loc=d3e48068-110394

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- Definition

Remaining balance of regulatory assets for which no return on investment during recovery is provided. In some cases, a regulator may permit an enterprise to include a cost that would be charged to expense by an unregulated enterprise as an allowable cost over a period of time by amortizing that cost for rate-making purposes, but the regulator does not include the unrecovered amount in the rate base.

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Reference 1: http://www.xbrl.org/2003/role/presentationRef
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-Name Accounting Standards Codification
-Topic 980
-SubTopic 340
-Section 50
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-Topic 980
-SubTopic 340
-Section 55
-Paragraph 2
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- Definition

Amount of operating expense for routine plant maintenance, repairs and operations of regulated operation.

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Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 225
-SubTopic 10
-Section S99
-Paragraph 2
-Subparagraph (SX 210.5-03.2(b))
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Regulatory Matters (Narrative) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Regulatory Matters [Line Items]
Regulatory liabilities	$ 1,493.2	$ 1,497.2
Refunded Federal Tax Reform benefits	66.0
Depreciation and amortization	506.9	461.8	$ 411.6
Revenue Subject to Refund [Member]
Regulatory Matters [Line Items]
Regulatory liabilities	20.0
IPL [Member]
Regulatory Matters [Line Items]
Regulatory assets not earning a return	77.0
Regulatory liabilities	754.9	755.4
Refunded Federal Tax Reform benefits	25.0
Other operation and maintenance	402.6	396.6	376.9
Depreciation and amortization	283.5	245.0	210.8
IPL [Member] \| Revenue Subject to Refund [Member]
Regulatory Matters [Line Items]
Regulatory liabilities	15.0
WPL [Member]
Regulatory Matters [Line Items]
Regulatory assets not earning a return	6.0
Regulatory liabilities	738.3	741.8
Refunded Federal Tax Reform benefits	41.0
Other operation and maintenance	241.6	238.5	209.6
Depreciation and amortization	219.4	212.9	$ 192.5
WPL [Member] \| Revenue Subject to Refund [Member]
Regulatory Matters [Line Items]
Regulatory liabilities	5.0
2016 Test Year Retail Electric [Member] \| IPL [Member]
Regulatory Matters [Line Items]
Interim rate increase (decrease), amount		$ 102.0
Interim rate increase (decrease), percentage		7.00%
Authorized increase (decrease) in final rates, amount	$ 130.0
Authorized increase (decrease) in final rates, percentage	9.00%
Write-down of regulatory assets		$ 9.0
2017/2018 Test Period Retail Electric [Member] \| WPL [Member]
Regulatory Matters [Line Items]
Authorized increase (decrease) in final rates, amount		9.0
Increase in base rates		60.0
Reduction in fuel-related costs		51.0
2017/2018 Test Period Retail Electric [Member] \| WPL [Member] \| Revenue Subject to Refund [Member]
Regulatory Matters [Line Items]
Regulatory liabilities	$ 20.0
2017/2018 Test Period Retail Gas [Member] \| WPL [Member]
Regulatory Matters [Line Items]
Authorized increase (decrease) in final rates, amount		9.0
Forward Contracts [Member] \| IUB [Member] \| IPL [Member]
Regulatory Matters [Line Items]
Recovery period, authorized	10 years
Sutherland Units 1 And 3 [Member] \| 2016 Test Year Retail Electric [Member] \| IPL [Member]
Regulatory Matters [Line Items]
Other operation and maintenance		4.0
Sutherland Units 1 And 3 [Member] \| IUB [Member] \| IPL [Member]
Regulatory Matters [Line Items]
Recovery period, authorized	10 years
AROs [Member] \| 2016 Test Year Retail Electric [Member] \| IPL [Member]
Regulatory Matters [Line Items]
Depreciation and amortization		$ 5.0
AROs [Member] \| IUB [Member] \| IPL [Member]
Regulatory Matters [Line Items]
Recovery period, authorized	4 years