Regulatory Matters (Tables)

9 Months Ended

Sep. 30, 2017

Regulatory Assets [Line Items]

Regulatory Assets

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

	Alliant Energy				IPL				WPL
	September 30, 2017		December 31, 2016		September 30, 2017		December 31, 2016		September 30, 2017		December 31, 2016
Tax-related		$1,147.9		$1,055.6		$1,107.9		$1,022.4		$40.0		$33.2
Pension and OPEB costs	547.8		578.7		279.3		294.0		268.5		284.7
Asset retirement obligations	107.9		105.9		71.9		64.3		36.0		41.6
EGUs retired early	67.4		41.4		32.9		—		34.5		41.4
Derivatives	49.9		30.7		22.3		10.0		27.6		20.7
Emission allowances	25.6		26.2		25.6		26.2		—		—
Other	90.0		76.6		51.0		41.9		39.0		34.7
		$2,036.5		$1,915.1		$1,590.9		$1,458.8		$445.6		$456.3

Regulatory Liabilities

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

	Alliant Energy				IPL				WPL
	September 30, 2017		December 31, 2016		September 30, 2017		December 31, 2016		September 30, 2017		December 31, 2016
Cost of removal obligations		$412.1		$411.6		$272.9		$269.4		$139.2		$142.2
Electric transmission cost recovery	94.8		72.0		35.9		35.7		58.9		36.3
IPL’s tax benefit riders	45.0		83.5		45.0		83.5		—		—
Commodity cost recovery	21.2		30.8		15.0		17.8		6.2		13.0
Energy efficiency cost recovery	20.0		20.5		—		—		20.0		20.5
Derivatives	10.9		31.5		5.8		12.1		5.1		19.4
Other	24.5		31.1		10.2		12.3		14.3		18.8
		$628.5		$681.0		$384.8		$430.8		$243.7		$250.2

Tax Benefit Riders

For the nine months ended September 30, 2017, Alliant Energy’s and IPL’s “IPL’s tax benefit riders” regulatory liabilities decreased by ($39) million as follows (in millions):

Electric tax benefit rider credits		($51	)
Gas tax benefit rider credits	(5		)
Rate-making accounting change	17
		($39	)

IPL [Member]

Regulatory Assets [Line Items]

Regulatory Assets

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

	Alliant Energy				IPL				WPL
	September 30, 2017		December 31, 2016		September 30, 2017		December 31, 2016		September 30, 2017		December 31, 2016
Tax-related		$1,147.9		$1,055.6		$1,107.9		$1,022.4		$40.0		$33.2
Pension and OPEB costs	547.8		578.7		279.3		294.0		268.5		284.7
Asset retirement obligations	107.9		105.9		71.9		64.3		36.0		41.6
EGUs retired early	67.4		41.4		32.9		—		34.5		41.4
Derivatives	49.9		30.7		22.3		10.0		27.6		20.7
Emission allowances	25.6		26.2		25.6		26.2		—		—
Other	90.0		76.6		51.0		41.9		39.0		34.7
		$2,036.5		$1,915.1		$1,590.9		$1,458.8		$445.6		$456.3

Regulatory Liabilities

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

	Alliant Energy				IPL				WPL
	September 30, 2017		December 31, 2016		September 30, 2017		December 31, 2016		September 30, 2017		December 31, 2016
Cost of removal obligations		$412.1		$411.6		$272.9		$269.4		$139.2		$142.2
Electric transmission cost recovery	94.8		72.0		35.9		35.7		58.9		36.3
IPL’s tax benefit riders	45.0		83.5		45.0		83.5		—		—
Commodity cost recovery	21.2		30.8		15.0		17.8		6.2		13.0
Energy efficiency cost recovery	20.0		20.5		—		—		20.0		20.5
Derivatives	10.9		31.5		5.8		12.1		5.1		19.4
Other	24.5		31.1		10.2		12.3		14.3		18.8
		$628.5		$681.0		$384.8		$430.8		$243.7		$250.2

Tax Benefit Riders

For the nine months ended September 30, 2017, Alliant Energy’s and IPL’s “IPL’s tax benefit riders” regulatory liabilities decreased by ($39) million as follows (in millions):

Electric tax benefit rider credits		($51	)
Gas tax benefit rider credits	(5		)
Rate-making accounting change	17
		($39	)

WPL [Member]

Regulatory Assets [Line Items]

Regulatory Assets

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

	Alliant Energy				IPL				WPL
	September 30, 2017		December 31, 2016		September 30, 2017		December 31, 2016		September 30, 2017		December 31, 2016
Tax-related		$1,147.9		$1,055.6		$1,107.9		$1,022.4		$40.0		$33.2
Pension and OPEB costs	547.8		578.7		279.3		294.0		268.5		284.7
Asset retirement obligations	107.9		105.9		71.9		64.3		36.0		41.6
EGUs retired early	67.4		41.4		32.9		—		34.5		41.4
Derivatives	49.9		30.7		22.3		10.0		27.6		20.7
Emission allowances	25.6		26.2		25.6		26.2		—		—
Other	90.0		76.6		51.0		41.9		39.0		34.7
		$2,036.5		$1,915.1		$1,590.9		$1,458.8		$445.6		$456.3

Regulatory Liabilities

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

	Alliant Energy				IPL				WPL
	September 30, 2017		December 31, 2016		September 30, 2017		December 31, 2016		September 30, 2017		December 31, 2016
Cost of removal obligations		$412.1		$411.6		$272.9		$269.4		$139.2		$142.2
Electric transmission cost recovery	94.8		72.0		35.9		35.7		58.9		36.3
IPL’s tax benefit riders	45.0		83.5		45.0		83.5		—		—
Commodity cost recovery	21.2		30.8		15.0		17.8		6.2		13.0
Energy efficiency cost recovery	20.0		20.5		—		—		20.0		20.5
Derivatives	10.9		31.5		5.8		12.1		5.1		19.4
Other	24.5		31.1		10.2		12.3		14.3		18.8
		$628.5		$681.0		$384.8		$430.8		$243.7		$250.2