Regulatory Matters (Tables)

12 Months Ended

Dec. 31, 2019

Regulatory Assets [Line Items]

Schedule of Regulatory Assets

At December 31, regulatory assets were comprised of the following items (in millions):

	Alliant Energy				IPL				WPL
	2019		2018		2019		2018		2019		2018
Tax-related		$817.6		$820.6		$776.8		$783.1		$40.8		$37.5
Pension and OPEB costs	524.0		542.3		262.5		274.0		261.5		268.3
Assets retired early	134.0		111.6		87.9		55.4		46.1		56.2
AROs	111.8		110.8		76.2		76.3		35.6		34.5
IPL’s DAEC PPA amendment	108.2		—		108.2		—		—		—
Derivatives	39.5		28.0		18.3		15.1		21.2		12.9
Emission allowances	21.1		23.6		21.1		23.6		—		—
Other	88.5		100.4		48.3		51.5		40.2		48.9
		$1,844.7		$1,737.3		$1,399.3		$1,279.0		$445.4		$458.3

Electric Generating Units Retired Early

Details regarding the recovery of the remaining net book value of these assets from IPL’s and WPL’s customers are as follows:

Entity	Asset	Retirement Date	Regulatory Asset Balance as of Dec. 31, 2019		Recovery	Regulatory Approval
IPL	Sutherland Units 1 and 3	2017		$28.5	Return of and return on remaining net book value over 10 years (return on effective with new rates expected to be implemented by the end of the first quarter of 2020)	IUB and FERC
IPL	M.L. Kapp Unit 2	2018	23.6		Return of and return on remaining net book value over 10 years	IUB and FERC
IPL	Analog electric meters	2019	35.8		Return of remaining net book value over 10 years (effective with new rates expected to be implemented by the end of the first quarter of 2020)	IUB
WPL	Nelson Dewey Units 1 and 2 and Edgewater Unit 3	2015	20.2		Return of and return on remaining net book value over 10 years	PSCW and FERC
WPL	Edgewater Unit 4	2018	25.9		Return of and return on remaining net book value over 10 years	PSCW and FERC

Schedule of Regulatory Liabilities

At December 31, regulatory liabilities were comprised of the following items (in millions):

	Alliant Energy				IPL				WPL
	2019		2018		2019		2018		2019		2018
Tax-related		$835.6		$890.6		$350.9		$390.1		$484.7		$500.5
Cost of removal obligations	387.7		401.2		257.0		273.3		130.7		127.9
Electric transmission cost recovery	88.6		104.0		51.3		47.7		37.3		56.3
Commodity cost recovery	24.2		16.8		8.8		11.9		15.4		4.9
WPL’s earnings sharing mechanism	21.9		25.4		—		—		21.9		25.4
Derivatives	19.9		18.5		17.4		10.2		2.5		8.3
Other	45.7		36.7		29.3		21.7		16.4		15.0
		$1,423.6		$1,493.2		$714.7		$754.9		$708.9		$738.3

IPL [Member]

Regulatory Assets [Line Items]

Schedule of Regulatory Assets

At December 31, regulatory assets were comprised of the following items (in millions):

	Alliant Energy				IPL				WPL
	2019		2018		2019		2018		2019		2018
Tax-related		$817.6		$820.6		$776.8		$783.1		$40.8		$37.5
Pension and OPEB costs	524.0		542.3		262.5		274.0		261.5		268.3
Assets retired early	134.0		111.6		87.9		55.4		46.1		56.2
AROs	111.8		110.8		76.2		76.3		35.6		34.5
IPL’s DAEC PPA amendment	108.2		—		108.2		—		—		—
Derivatives	39.5		28.0		18.3		15.1		21.2		12.9
Emission allowances	21.1		23.6		21.1		23.6		—		—
Other	88.5		100.4		48.3		51.5		40.2		48.9
		$1,844.7		$1,737.3		$1,399.3		$1,279.0		$445.4		$458.3

Electric Generating Units Retired Early

Details regarding the recovery of the remaining net book value of these assets from IPL’s and WPL’s customers are as follows:

Entity	Asset	Retirement Date	Regulatory Asset Balance as of Dec. 31, 2019		Recovery	Regulatory Approval
IPL	Sutherland Units 1 and 3	2017		$28.5	Return of and return on remaining net book value over 10 years (return on effective with new rates expected to be implemented by the end of the first quarter of 2020)	IUB and FERC
IPL	M.L. Kapp Unit 2	2018	23.6		Return of and return on remaining net book value over 10 years	IUB and FERC
IPL	Analog electric meters	2019	35.8		Return of remaining net book value over 10 years (effective with new rates expected to be implemented by the end of the first quarter of 2020)	IUB
WPL	Nelson Dewey Units 1 and 2 and Edgewater Unit 3	2015	20.2		Return of and return on remaining net book value over 10 years	PSCW and FERC
WPL	Edgewater Unit 4	2018	25.9		Return of and return on remaining net book value over 10 years	PSCW and FERC

Schedule of Regulatory Liabilities

At December 31, regulatory liabilities were comprised of the following items (in millions):

	Alliant Energy				IPL				WPL
	2019		2018		2019		2018		2019		2018
Tax-related		$835.6		$890.6		$350.9		$390.1		$484.7		$500.5
Cost of removal obligations	387.7		401.2		257.0		273.3		130.7		127.9
Electric transmission cost recovery	88.6		104.0		51.3		47.7		37.3		56.3
Commodity cost recovery	24.2		16.8		8.8		11.9		15.4		4.9
WPL’s earnings sharing mechanism	21.9		25.4		—		—		21.9		25.4
Derivatives	19.9		18.5		17.4		10.2		2.5		8.3
Other	45.7		36.7		29.3		21.7		16.4		15.0
		$1,423.6		$1,493.2		$714.7		$754.9		$708.9		$738.3

WPL [Member]

Regulatory Assets [Line Items]

Schedule of Regulatory Assets

At December 31, regulatory assets were comprised of the following items (in millions):

	Alliant Energy				IPL				WPL
	2019		2018		2019		2018		2019		2018
Tax-related		$817.6		$820.6		$776.8		$783.1		$40.8		$37.5
Pension and OPEB costs	524.0		542.3		262.5		274.0		261.5		268.3
Assets retired early	134.0		111.6		87.9		55.4		46.1		56.2
AROs	111.8		110.8		76.2		76.3		35.6		34.5
IPL’s DAEC PPA amendment	108.2		—		108.2		—		—		—
Derivatives	39.5		28.0		18.3		15.1		21.2		12.9
Emission allowances	21.1		23.6		21.1		23.6		—		—
Other	88.5		100.4		48.3		51.5		40.2		48.9
		$1,844.7		$1,737.3		$1,399.3		$1,279.0		$445.4		$458.3

Electric Generating Units Retired Early

Details regarding the recovery of the remaining net book value of these assets from IPL’s and WPL’s customers are as follows:

Entity	Asset	Retirement Date	Regulatory Asset Balance as of Dec. 31, 2019		Recovery	Regulatory Approval
IPL	Sutherland Units 1 and 3	2017		$28.5	Return of and return on remaining net book value over 10 years (return on effective with new rates expected to be implemented by the end of the first quarter of 2020)	IUB and FERC
IPL	M.L. Kapp Unit 2	2018	23.6		Return of and return on remaining net book value over 10 years	IUB and FERC
IPL	Analog electric meters	2019	35.8		Return of remaining net book value over 10 years (effective with new rates expected to be implemented by the end of the first quarter of 2020)	IUB
WPL	Nelson Dewey Units 1 and 2 and Edgewater Unit 3	2015	20.2		Return of and return on remaining net book value over 10 years	PSCW and FERC
WPL	Edgewater Unit 4	2018	25.9		Return of and return on remaining net book value over 10 years	PSCW and FERC

Schedule of Regulatory Liabilities

At December 31, regulatory liabilities were comprised of the following items (in millions):

	Alliant Energy				IPL				WPL
	2019		2018		2019		2018		2019		2018
Tax-related		$835.6		$890.6		$350.9		$390.1		$484.7		$500.5
Cost of removal obligations	387.7		401.2		257.0		273.3		130.7		127.9
Electric transmission cost recovery	88.6		104.0		51.3		47.7		37.3		56.3
Commodity cost recovery	24.2		16.8		8.8		11.9		15.4		4.9
WPL’s earnings sharing mechanism	21.9		25.4		—		—		21.9		25.4
Derivatives	19.9		18.5		17.4		10.2		2.5		8.3
Other	45.7		36.7		29.3		21.7		16.4		15.0
		$1,423.6		$1,493.2		$714.7		$754.9		$708.9		$738.3