Regulatory Matters (Tables)

6 Months Ended

Jun. 30, 2017

Regulatory Assets [Line Items]

Regulatory Assets

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

	Alliant Energy				IPL				WPL
	June 30, 2017		December 31, 2016		June 30, 2017		December 31, 2016		June 30, 2017		December 31, 2016
Tax-related		$1,100.7		$1,055.6		$1,063.3		$1,022.4		$37.4		$33.2
Pension and OPEB costs	558.3		578.7		284.2		294.0		274.1		284.7
Asset retirement obligations	108.7		105.9		72.5		64.3		36.2		41.6
EGUs retired early	78.2		41.4		40.3		—		37.9		41.4
Derivatives	47.9		30.7		18.1		10.0		29.8		20.7
Emission allowances	25.9		26.2		25.9		26.2		—		—
Other	96.3		76.6		52.3		41.9		44.0		34.7
		$2,016.0		$1,915.1		$1,556.6		$1,458.8		$459.4		$456.3

Regulatory Liabilities

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

	Alliant Energy				IPL				WPL
	June 30, 2017		December 31, 2016		June 30, 2017		December 31, 2016		June 30, 2017		December 31, 2016
Cost of removal obligations		$415.3		$411.6		$273.0		$269.4		$142.3		$142.2
Electric transmission cost recovery	118.5		72.0		61.7		35.7		56.8		36.3
IPL’s tax benefit riders	47.2		83.5		47.2		83.5		—		—
Commodity cost recovery	27.5		30.8		15.9		17.8		11.6		13.0
Energy efficiency cost recovery	19.6		20.5		—		—		19.6		20.5
Derivatives	11.4		31.5		7.1		12.1		4.3		19.4
Other	26.3		31.1		10.8		12.3		15.5		18.8
		$665.8		$681.0		$415.7		$430.8		$250.1		$250.2

Tax Benefit Riders

For the six months ended June 30, 2017, Alliant Energy’s and IPL’s “IPL’s tax benefit riders” regulatory liabilities decreased by $36 million as follows (in millions):

Electric tax benefit rider credits		$33
Gas tax benefit rider credits	3
		$36

IPL [Member]

Regulatory Assets [Line Items]

Regulatory Assets

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

	Alliant Energy				IPL				WPL
	June 30, 2017		December 31, 2016		June 30, 2017		December 31, 2016		June 30, 2017		December 31, 2016
Tax-related		$1,100.7		$1,055.6		$1,063.3		$1,022.4		$37.4		$33.2
Pension and OPEB costs	558.3		578.7		284.2		294.0		274.1		284.7
Asset retirement obligations	108.7		105.9		72.5		64.3		36.2		41.6
EGUs retired early	78.2		41.4		40.3		—		37.9		41.4
Derivatives	47.9		30.7		18.1		10.0		29.8		20.7
Emission allowances	25.9		26.2		25.9		26.2		—		—
Other	96.3		76.6		52.3		41.9		44.0		34.7
		$2,016.0		$1,915.1		$1,556.6		$1,458.8		$459.4		$456.3

Regulatory Liabilities

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

	Alliant Energy				IPL				WPL
	June 30, 2017		December 31, 2016		June 30, 2017		December 31, 2016		June 30, 2017		December 31, 2016
Cost of removal obligations		$415.3		$411.6		$273.0		$269.4		$142.3		$142.2
Electric transmission cost recovery	118.5		72.0		61.7		35.7		56.8		36.3
IPL’s tax benefit riders	47.2		83.5		47.2		83.5		—		—
Commodity cost recovery	27.5		30.8		15.9		17.8		11.6		13.0
Energy efficiency cost recovery	19.6		20.5		—		—		19.6		20.5
Derivatives	11.4		31.5		7.1		12.1		4.3		19.4
Other	26.3		31.1		10.8		12.3		15.5		18.8
		$665.8		$681.0		$415.7		$430.8		$250.1		$250.2

Tax Benefit Riders

For the six months ended June 30, 2017, Alliant Energy’s and IPL’s “IPL’s tax benefit riders” regulatory liabilities decreased by $36 million as follows (in millions):

Electric tax benefit rider credits		$33
Gas tax benefit rider credits	3
		$36

WPL [Member]

Regulatory Assets [Line Items]

Regulatory Assets

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

	Alliant Energy				IPL				WPL
	June 30, 2017		December 31, 2016		June 30, 2017		December 31, 2016		June 30, 2017		December 31, 2016
Tax-related		$1,100.7		$1,055.6		$1,063.3		$1,022.4		$37.4		$33.2
Pension and OPEB costs	558.3		578.7		284.2		294.0		274.1		284.7
Asset retirement obligations	108.7		105.9		72.5		64.3		36.2		41.6
EGUs retired early	78.2		41.4		40.3		—		37.9		41.4
Derivatives	47.9		30.7		18.1		10.0		29.8		20.7
Emission allowances	25.9		26.2		25.9		26.2		—		—
Other	96.3		76.6		52.3		41.9		44.0		34.7
		$2,016.0		$1,915.1		$1,556.6		$1,458.8		$459.4		$456.3

Regulatory Liabilities

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

	Alliant Energy				IPL				WPL
	June 30, 2017		December 31, 2016		June 30, 2017		December 31, 2016		June 30, 2017		December 31, 2016
Cost of removal obligations		$415.3		$411.6		$273.0		$269.4		$142.3		$142.2
Electric transmission cost recovery	118.5		72.0		61.7		35.7		56.8		36.3
IPL’s tax benefit riders	47.2		83.5		47.2		83.5		—		—
Commodity cost recovery	27.5		30.8		15.9		17.8		11.6		13.0
Energy efficiency cost recovery	19.6		20.5		—		—		19.6		20.5
Derivatives	11.4		31.5		7.1		12.1		4.3		19.4
Other	26.3		31.1		10.8		12.3		15.5		18.8
		$665.8		$681.0		$415.7		$430.8		$250.1		$250.2