Regulatory Matters (Tables)

6 Months Ended

Jun. 30, 2018

Regulatory Assets [Line Items]

Regulatory Assets

Regulatory assets were comprised of the following items (in millions):

	Alliant Energy				IPL				WPL
	June 30, 2018		December 31, 2017		June 30, 2018		December 31, 2017		June 30, 2018		December 31, 2017
Tax-related		$776.0		$778.2		$742.2		$750.5		$33.8		$27.7
Pension and OPEB costs	529.2		548.0		265.6		274.4		263.6		273.6
Asset retirement obligations	109.8		109.3		76.3		72.5		33.5		36.8
EGUs retired early	91.2		63.8		60.2		31.6		31.0		32.2
Derivatives	49.4		45.3		27.9		21.8		21.5		23.5
Emission allowances	24.9		25.5		24.9		25.5		—		—
Other	97.9		96.6		52.1		55.3		45.8		41.3
		$1,678.4		$1,666.7		$1,249.2		$1,231.6		$429.2		$435.1

Regulatory Liabilities

Regulatory liabilities were comprised of the following items (in millions):

	Alliant Energy				IPL				WPL
	June 30, 2018		December 31, 2017		June 30, 2018		December 31, 2017		June 30, 2018		December 31, 2017
Tax-related		$908.4		$899.4		$406.8		$399.5		$501.6		$499.9
Cost of removal obligations	402.4		410.0		274.9		274.5		127.5		135.5
Electric transmission cost recovery	105.6		90.4		41.1		26.4		64.5		64.0
Commodity cost recovery	25.7		21.0		20.4		14.6		5.3		6.4
IPL’s tax benefit riders	19.8		25.0		19.8		25.0		—		—
Other	51.0		51.4		11.8		15.4		39.2		36.0
		$1,512.9		$1,497.2		$774.8		$755.4		$738.1		$741.8

IPL [Member]

Regulatory Assets [Line Items]

Regulatory Assets

Regulatory assets were comprised of the following items (in millions):

	Alliant Energy				IPL				WPL
	June 30, 2018		December 31, 2017		June 30, 2018		December 31, 2017		June 30, 2018		December 31, 2017
Tax-related		$776.0		$778.2		$742.2		$750.5		$33.8		$27.7
Pension and OPEB costs	529.2		548.0		265.6		274.4		263.6		273.6
Asset retirement obligations	109.8		109.3		76.3		72.5		33.5		36.8
EGUs retired early	91.2		63.8		60.2		31.6		31.0		32.2
Derivatives	49.4		45.3		27.9		21.8		21.5		23.5
Emission allowances	24.9		25.5		24.9		25.5		—		—
Other	97.9		96.6		52.1		55.3		45.8		41.3
		$1,678.4		$1,666.7		$1,249.2		$1,231.6		$429.2		$435.1

Regulatory Liabilities

Regulatory liabilities were comprised of the following items (in millions):

	Alliant Energy				IPL				WPL
	June 30, 2018		December 31, 2017		June 30, 2018		December 31, 2017		June 30, 2018		December 31, 2017
Tax-related		$908.4		$899.4		$406.8		$399.5		$501.6		$499.9
Cost of removal obligations	402.4		410.0		274.9		274.5		127.5		135.5
Electric transmission cost recovery	105.6		90.4		41.1		26.4		64.5		64.0
Commodity cost recovery	25.7		21.0		20.4		14.6		5.3		6.4
IPL’s tax benefit riders	19.8		25.0		19.8		25.0		—		—
Other	51.0		51.4		11.8		15.4		39.2		36.0
		$1,512.9		$1,497.2		$774.8		$755.4		$738.1		$741.8

WPL [Member]

Regulatory Assets [Line Items]

Regulatory Assets

Regulatory assets were comprised of the following items (in millions):

	Alliant Energy				IPL				WPL
	June 30, 2018		December 31, 2017		June 30, 2018		December 31, 2017		June 30, 2018		December 31, 2017
Tax-related		$776.0		$778.2		$742.2		$750.5		$33.8		$27.7
Pension and OPEB costs	529.2		548.0		265.6		274.4		263.6		273.6
Asset retirement obligations	109.8		109.3		76.3		72.5		33.5		36.8
EGUs retired early	91.2		63.8		60.2		31.6		31.0		32.2
Derivatives	49.4		45.3		27.9		21.8		21.5		23.5
Emission allowances	24.9		25.5		24.9		25.5		—		—
Other	97.9		96.6		52.1		55.3		45.8		41.3
		$1,678.4		$1,666.7		$1,249.2		$1,231.6		$429.2		$435.1

Regulatory Liabilities

Regulatory liabilities were comprised of the following items (in millions):

	Alliant Energy				IPL				WPL
	June 30, 2018		December 31, 2017		June 30, 2018		December 31, 2017		June 30, 2018		December 31, 2017
Tax-related		$908.4		$899.4		$406.8		$399.5		$501.6		$499.9
Cost of removal obligations	402.4		410.0		274.9		274.5		127.5		135.5
Electric transmission cost recovery	105.6		90.4		41.1		26.4		64.5		64.0
Commodity cost recovery	25.7		21.0		20.4		14.6		5.3		6.4
IPL’s tax benefit riders	19.8		25.0		19.8		25.0		—		—
Other	51.0		51.4		11.8		15.4		39.2		36.0
		$1,512.9		$1,497.2		$774.8		$755.4		$738.1		$741.8