Jointly-Owned Electric Utility Plant (Tables)

12 Months Ended

Dec. 31, 2018

Jointly Owned Electric Utility Plant [Line Items]

Components of Jointly-Owned Electric Utility Plants

Information relative to IPL’s and WPL’s ownership interest in these jointly-owned EGUs at December 31, 2018 was as follows (dollars in millions):

	Ownership		Electric		Accumulated Provision		Construction
	Interest %		Plant		for Depreciation		Work in Progress
IPL
Ottumwa Unit 1	48.0	%		$507.1		$161.7		$65.3
George Neal Unit 4	25.7	%	187.3		89.8		1.2
George Neal Unit 3	28.0	%	156.7		57.8		1.4
Louisa Unit 1	4.0	%	39.2		23.9		0.8
			890.3		333.2		68.7
WPL
Columbia Units 1-2	52.5	%	779.4		247.9		9.8
FWEC	42.6	%	119.7		41.2		0.1
West Riverside (a)	91.8	%	—		—		538.4
			899.1		289.1		548.3
Alliant Energy				$1,789.4		$622.3		$617.0

(a) In January 2018, certain electric cooperatives, which currently have wholesale power supply agreements with WPL, acquired a partial ownership interest in West Riverside.

IPL [Member]

Jointly Owned Electric Utility Plant [Line Items]

Components of Jointly-Owned Electric Utility Plants

Information relative to IPL’s and WPL’s ownership interest in these jointly-owned EGUs at December 31, 2018 was as follows (dollars in millions):

	Ownership		Electric		Accumulated Provision		Construction
	Interest %		Plant		for Depreciation		Work in Progress
IPL
Ottumwa Unit 1	48.0	%		$507.1		$161.7		$65.3
George Neal Unit 4	25.7	%	187.3		89.8		1.2
George Neal Unit 3	28.0	%	156.7		57.8		1.4
Louisa Unit 1	4.0	%	39.2		23.9		0.8
			890.3		333.2		68.7
WPL
Columbia Units 1-2	52.5	%	779.4		247.9		9.8
FWEC	42.6	%	119.7		41.2		0.1
West Riverside (a)	91.8	%	—		—		538.4
			899.1		289.1		548.3
Alliant Energy				$1,789.4		$622.3		$617.0

(a) In January 2018, certain electric cooperatives, which currently have wholesale power supply agreements with WPL, acquired a partial ownership interest in West Riverside.

WPL [Member]

Jointly Owned Electric Utility Plant [Line Items]

Components of Jointly-Owned Electric Utility Plants

Information relative to IPL’s and WPL’s ownership interest in these jointly-owned EGUs at December 31, 2018 was as follows (dollars in millions):

	Ownership		Electric		Accumulated Provision		Construction
	Interest %		Plant		for Depreciation		Work in Progress
IPL
Ottumwa Unit 1	48.0	%		$507.1		$161.7		$65.3
George Neal Unit 4	25.7	%	187.3		89.8		1.2
George Neal Unit 3	28.0	%	156.7		57.8		1.4
Louisa Unit 1	4.0	%	39.2		23.9		0.8
			890.3		333.2		68.7
WPL
Columbia Units 1-2	52.5	%	779.4		247.9		9.8
FWEC	42.6	%	119.7		41.2		0.1
West Riverside (a)	91.8	%	—		—		538.4
			899.1		289.1		548.3
Alliant Energy				$1,789.4		$622.3		$617.0

(a) In January 2018, certain electric cooperatives, which currently have wholesale power supply agreements with WPL, acquired a partial ownership interest in West Riverside.