Jointly-Owned Electric Utility Plant (Details) $ in Millions	Dec. 31, 2020 USD ($)
Jointly Owned Electric Utility Plant [Line Items]
Electric Plant	$ 2,574
Accumulated Provision for Depreciation	727
Construction Work in Progress	41
IPL [Member]
Jointly Owned Electric Utility Plant [Line Items]
Electric Plant	982
Accumulated Provision for Depreciation	380
Construction Work in Progress	24
WPL [Member]
Jointly Owned Electric Utility Plant [Line Items]
Electric Plant	1,592
Accumulated Provision for Depreciation	347
Construction Work in Progress	$ 17
Ottumwa Unit 1 [Member] \| IPL [Member]
Jointly Owned Electric Utility Plant [Line Items]
Ownership Interest %	48.00%
Electric Plant	$ 580
Accumulated Provision for Depreciation	195
Construction Work in Progress	$ 22
George Neal Unit 4 [Member] \| IPL [Member]
Jointly Owned Electric Utility Plant [Line Items]
Ownership Interest %	25.70%
Electric Plant	$ 192
Accumulated Provision for Depreciation	96
Construction Work in Progress	$ 2
George Neal Unit 3 [Member] \| IPL [Member]
Jointly Owned Electric Utility Plant [Line Items]
Ownership Interest %	28.00%
Electric Plant	$ 171
Accumulated Provision for Depreciation	67
Construction Work in Progress	$ 0
Louisa Unit 1 [Member] \| IPL [Member]
Jointly Owned Electric Utility Plant [Line Items]
Ownership Interest %	4.00%
Electric Plant	$ 39
Accumulated Provision for Depreciation	22
Construction Work in Progress	$ 0
Columbia Units 1-2 [Member] \| WPL [Member]
Jointly Owned Electric Utility Plant [Line Items]
Ownership Interest %	53.50%
Electric Plant	$ 786
Accumulated Provision for Depreciation	289
Construction Work in Progress	$ 4
West Riverside [Member] \| WPL [Member]
Jointly Owned Electric Utility Plant [Line Items]
Ownership Interest %	91.80%
Electric Plant	$ 686
Accumulated Provision for Depreciation	12
Construction Work in Progress	$ 13
Forward Wind Energy Center [Member] \| WPL [Member]
Jointly Owned Electric Utility Plant [Line Items]
Ownership Interest %	42.60%
Electric Plant	$ 120
Accumulated Provision for Depreciation	46
Construction Work in Progress	$ 0

The period end amount owned by the reporting utility of a jointly owned utility plant in service.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 980
-SubTopic 360
-Section S99
-Paragraph 1
-Subparagraph (SAB Topic 10.C)
-URI http://asc.fasb.org/extlink&oid=115995737&loc=d3e659983-123033

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+ References

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The period end amount of construction work in progress at a jointly owned electricity generation plant.

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- Definition

The period end amount of accumulated depreciation in a jointly owned electricity generation plant.

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- Definition

The proportionate share of interest (percent) in a jointly owned utility plant.

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