Investments (Tables)

12 Months Ended

Dec. 31, 2018

Investment [Line Items]

Unconsolidated Equity Investments

Unconsolidated investments accounted for under the equity method of accounting are as follows (in millions):

	Ownership Interest at	Carrying Value at December 31,				Equity (Income) / Loss
	December 31, 2018	2018		2017		2018			2017			2016
Alliant Energy
ATC Holdings (a)	16%-20%		$293.6		$274.2		($38.1	)		($42.4	)		($39.1	)
Non-utility wind farm in Oklahoma	50%	105.1		98.3		(15.6		)	(1.8		)	—
Other	Various	22.6		8.9		(0.9		)	(0.6		)	(0.5		)
			$421.3		$381.4		($54.6	)		($44.8	)		($39.6	)
WPL
ATC	—%		$—		$—		$—			$—			($39.1	)
Wisconsin River Power Company	50%	8.1		8.3		(0.9		)	(0.7		)	(0.7		)
			$8.1		$8.3		($0.9	)		($0.7	)		($39.8	)

(a) As of December 31, 2018, Alliant Energy’s interest in ATC Holdings is comprised of a 16% ownership interest in ATC and a 20% ownership interest in ATC Holdco LLC, which are described below. Alliant Energy currently has the ability to exercise significant influence over ATC’s and ATC Holdco LLC’s financial and operating policies through its participation on ATC’s Board of Directors.

Summary Aggregate Financial Information

Summary aggregate financial information from the financial statements of these holdings is as follows (in millions):

	Alliant Energy						WPL
	2018		2017		2016		2018		2017		2016
Revenues		$724		$741		$658		$8		$8		$658
Operating income	325		374		331		2		4		331
Net income	217		267		232		1		2		234
As of December 31:
Current assets	144		104				4		7
Non-current assets	5,498		5,041				19		20
Current liabilities	644		770				1		2
Non-current liabilities	2,315		2,038				6		8
Noncontrolling interest	223		255				—		—

WPL [Member]

Investment [Line Items]

Unconsolidated Equity Investments

Unconsolidated investments accounted for under the equity method of accounting are as follows (in millions):

	Ownership Interest at	Carrying Value at December 31,				Equity (Income) / Loss
	December 31, 2018	2018		2017		2018			2017			2016
Alliant Energy
ATC Holdings (a)	16%-20%		$293.6		$274.2		($38.1	)		($42.4	)		($39.1	)
Non-utility wind farm in Oklahoma	50%	105.1		98.3		(15.6		)	(1.8		)	—
Other	Various	22.6		8.9		(0.9		)	(0.6		)	(0.5		)
			$421.3		$381.4		($54.6	)		($44.8	)		($39.6	)
WPL
ATC	—%		$—		$—		$—			$—			($39.1	)
Wisconsin River Power Company	50%	8.1		8.3		(0.9		)	(0.7		)	(0.7		)
			$8.1		$8.3		($0.9	)		($0.7	)		($39.8	)

(a) As of December 31, 2018, Alliant Energy’s interest in ATC Holdings is comprised of a 16% ownership interest in ATC and a 20% ownership interest in ATC Holdco LLC, which are described below. Alliant Energy currently has the ability to exercise significant influence over ATC’s and ATC Holdco LLC’s financial and operating policies through its participation on ATC’s Board of Directors.

Summary Aggregate Financial Information

Summary aggregate financial information from the financial statements of these holdings is as follows (in millions):

	Alliant Energy						WPL
	2018		2017		2016		2018		2017		2016
Revenues		$724		$741		$658		$8		$8		$658
Operating income	325		374		331		2		4		331
Net income	217		267		232		1		2		234
As of December 31:
Current assets	144		104				4		7
Non-current assets	5,498		5,041				19		20
Current liabilities	644		770				1		2
Non-current liabilities	2,315		2,038				6		8
Noncontrolling interest	223		255				—		—