Regulatory Matters (Tables)

3 Months Ended

Mar. 31, 2018

Regulatory Assets [Line Items]

Regulatory Assets

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

	Alliant Energy				IPL				WPL
	March 31, 2018		December 31, 2017		March 31, 2018		December 31, 2017		March 31, 2018		December 31, 2017
Tax-related		$795.1		$778.2		$762.8		$750.5		$32.3		$27.7
Pension and OPEB costs	538.6		548.0		270.0		274.4		268.6		273.6
Asset retirement obligations	104.3		109.3		67.9		72.5		36.4		36.8
EGUs retired early	60.1		63.8		30.4		31.6		29.7		32.2
Derivatives	47.6		45.3		25.5		21.8		22.1		23.5
Emission allowances	25.4		25.5		25.4		25.5		—		—
Other	93.0		96.6		48.9		55.3		44.1		41.3
		$1,664.1		$1,666.7		$1,230.9		$1,231.6		$433.2		$435.1

Regulatory Liabilities

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

	Alliant Energy				IPL				WPL
	March 31, 2018		December 31, 2017		March 31, 2018		December 31, 2017		March 31, 2018		December 31, 2017
Tax-related		$901.3		$899.4		$399.5		$399.5		$501.8		$499.9
Cost of removal obligations	415.6		410.0		274.7		274.5		140.9		135.5
Electric transmission cost recovery	95.3		90.4		33.5		26.4		61.8		64.0
Commodity cost recovery	31.2		21.0		24.2		14.6		7.0		6.4
IPL’s tax benefit riders	25.0		25.0		25.0		25.0		—		—
Other	69.5		51.4		20.4		15.4		49.1		36.0
		$1,537.9		$1,497.2		$777.3		$755.4		$760.6		$741.8

IPL [Member]

Regulatory Assets [Line Items]

Regulatory Assets

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

	Alliant Energy				IPL				WPL
	March 31, 2018		December 31, 2017		March 31, 2018		December 31, 2017		March 31, 2018		December 31, 2017
Tax-related		$795.1		$778.2		$762.8		$750.5		$32.3		$27.7
Pension and OPEB costs	538.6		548.0		270.0		274.4		268.6		273.6
Asset retirement obligations	104.3		109.3		67.9		72.5		36.4		36.8
EGUs retired early	60.1		63.8		30.4		31.6		29.7		32.2
Derivatives	47.6		45.3		25.5		21.8		22.1		23.5
Emission allowances	25.4		25.5		25.4		25.5		—		—
Other	93.0		96.6		48.9		55.3		44.1		41.3
		$1,664.1		$1,666.7		$1,230.9		$1,231.6		$433.2		$435.1

Regulatory Liabilities

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

	Alliant Energy				IPL				WPL
	March 31, 2018		December 31, 2017		March 31, 2018		December 31, 2017		March 31, 2018		December 31, 2017
Tax-related		$901.3		$899.4		$399.5		$399.5		$501.8		$499.9
Cost of removal obligations	415.6		410.0		274.7		274.5		140.9		135.5
Electric transmission cost recovery	95.3		90.4		33.5		26.4		61.8		64.0
Commodity cost recovery	31.2		21.0		24.2		14.6		7.0		6.4
IPL’s tax benefit riders	25.0		25.0		25.0		25.0		—		—
Other	69.5		51.4		20.4		15.4		49.1		36.0
		$1,537.9		$1,497.2		$777.3		$755.4		$760.6		$741.8

WPL [Member]

Regulatory Assets [Line Items]

Regulatory Assets

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

	Alliant Energy				IPL				WPL
	March 31, 2018		December 31, 2017		March 31, 2018		December 31, 2017		March 31, 2018		December 31, 2017
Tax-related		$795.1		$778.2		$762.8		$750.5		$32.3		$27.7
Pension and OPEB costs	538.6		548.0		270.0		274.4		268.6		273.6
Asset retirement obligations	104.3		109.3		67.9		72.5		36.4		36.8
EGUs retired early	60.1		63.8		30.4		31.6		29.7		32.2
Derivatives	47.6		45.3		25.5		21.8		22.1		23.5
Emission allowances	25.4		25.5		25.4		25.5		—		—
Other	93.0		96.6		48.9		55.3		44.1		41.3
		$1,664.1		$1,666.7		$1,230.9		$1,231.6		$433.2		$435.1

Regulatory Liabilities

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

	Alliant Energy				IPL				WPL
	March 31, 2018		December 31, 2017		March 31, 2018		December 31, 2017		March 31, 2018		December 31, 2017
Tax-related		$901.3		$899.4		$399.5		$399.5		$501.8		$499.9
Cost of removal obligations	415.6		410.0		274.7		274.5		140.9		135.5
Electric transmission cost recovery	95.3		90.4		33.5		26.4		61.8		64.0
Commodity cost recovery	31.2		21.0		24.2		14.6		7.0		6.4
IPL’s tax benefit riders	25.0		25.0		25.0		25.0		—		—
Other	69.5		51.4		20.4		15.4		49.1		36.0
		$1,537.9		$1,497.2		$777.3		$755.4		$760.6		$741.8