Jointly-Owned Electric Utility Plant (Tables)

12 Months Ended

Dec. 31, 2017

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 coal-fired EGUs at December 31, 2017 was as follows (dollars in millions):

	Ownership		Electric		Accumulated Provision		Construction
	Interest %		Plant		for Depreciation		Work in Progress
IPL
Ottumwa Unit 1	48.0	%		$501.8		$144.9		$37.3
George Neal Unit 4	25.7	%	187.2		85.2		0.8
George Neal Unit 3	28.0	%	150.6		53.0		2.5
Louisa Unit 1	4.0	%	37.8		22.4		1.4
			877.4		305.5		42.0
WPL
Columbia Units 1-2	50.1	%	714.7		216.8		46.9
Edgewater Unit 4	68.2	%	99.9		60.4		0.1
			814.6		277.2		47.0
Alliant Energy				$1,692.0		$582.7		$89.0

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 coal-fired EGUs at December 31, 2017 was as follows (dollars in millions):

	Ownership		Electric		Accumulated Provision		Construction
	Interest %		Plant		for Depreciation		Work in Progress
IPL
Ottumwa Unit 1	48.0	%		$501.8		$144.9		$37.3
George Neal Unit 4	25.7	%	187.2		85.2		0.8
George Neal Unit 3	28.0	%	150.6		53.0		2.5
Louisa Unit 1	4.0	%	37.8		22.4		1.4
			877.4		305.5		42.0
WPL
Columbia Units 1-2	50.1	%	714.7		216.8		46.9
Edgewater Unit 4	68.2	%	99.9		60.4		0.1
			814.6		277.2		47.0
Alliant Energy				$1,692.0		$582.7		$89.0

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 coal-fired EGUs at December 31, 2017 was as follows (dollars in millions):

	Ownership		Electric		Accumulated Provision		Construction
	Interest %		Plant		for Depreciation		Work in Progress
IPL
Ottumwa Unit 1	48.0	%		$501.8		$144.9		$37.3
George Neal Unit 4	25.7	%	187.2		85.2		0.8
George Neal Unit 3	28.0	%	150.6		53.0		2.5
Louisa Unit 1	4.0	%	37.8		22.4		1.4
			877.4		305.5		42.0
WPL
Columbia Units 1-2	50.1	%	714.7		216.8		46.9
Edgewater Unit 4	68.2	%	99.9		60.4		0.1
			814.6		277.2		47.0
Alliant Energy				$1,692.0		$582.7		$89.0