Regulatory Matters (Tables)

3 Months Ended

Mar. 31, 2017

Regulatory Assets [Line Items]

Regulatory Assets

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

	Alliant Energy				IPL				WPL
	March 31, 2017		December 31, 2016		March 31, 2017		December 31, 2016		March 31, 2017		December 31, 2016
Tax-related		$1,080.2		$1,055.6		$1,044.9		$1,022.4		$35.3		$33.2
Pension and OPEB costs	568.5		578.7		289.1		294.0		279.4		284.7
Asset retirement obligations	108.6		105.9		67.1		64.3		41.5		41.6
Derivatives	46.4		30.7		17.2		10.0		29.2		20.7
WPL’s EGUs retired early	39.7		41.4		—		—		39.7		41.4
Emission allowances	26.0		26.2		26.0		26.2		—		—
Other	93.6		76.6		56.5		41.9		37.1		34.7
		$1,963.0		$1,915.1		$1,500.8		$1,458.8		$462.2		$456.3

Regulatory Liabilities

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

	Alliant Energy				IPL				WPL
	March 31, 2017		December 31, 2016		March 31, 2017		December 31, 2016		March 31, 2017		December 31, 2016
Cost of removal obligations		$413.0		$411.6		$271.1		$269.4		$141.9		$142.2
Electric transmission cost recovery	128.3		72.0		75.9		35.7		52.4		36.3
IPL’s tax benefit riders	64.7		83.5		64.7		83.5		—		—
Commodity cost recovery	32.9		30.8		20.1		17.8		12.8		13.0
Energy efficiency cost recovery	20.6		20.5		—		—		20.6		20.5
Derivatives	9.0		31.5		5.1		12.1		3.9		19.4
Other	28.1		31.1		11.4		12.3		16.7		18.8
		$696.6		$681.0		$448.3		$430.8		$248.3		$250.2

Tax Benefit Riders

For the three months ended March 31, 2017, Alliant Energy’s and IPL’s “IPL’s tax benefit riders” regulatory liabilities decreased by $19 million as follows (in millions):

Electric tax benefit rider credits		$17
Gas tax benefit rider credits	2
		$19

IPL [Member]

Regulatory Assets [Line Items]

Regulatory Assets

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

	Alliant Energy				IPL				WPL
	March 31, 2017		December 31, 2016		March 31, 2017		December 31, 2016		March 31, 2017		December 31, 2016
Tax-related		$1,080.2		$1,055.6		$1,044.9		$1,022.4		$35.3		$33.2
Pension and OPEB costs	568.5		578.7		289.1		294.0		279.4		284.7
Asset retirement obligations	108.6		105.9		67.1		64.3		41.5		41.6
Derivatives	46.4		30.7		17.2		10.0		29.2		20.7
WPL’s EGUs retired early	39.7		41.4		—		—		39.7		41.4
Emission allowances	26.0		26.2		26.0		26.2		—		—
Other	93.6		76.6		56.5		41.9		37.1		34.7
		$1,963.0		$1,915.1		$1,500.8		$1,458.8		$462.2		$456.3

Regulatory Liabilities

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

	Alliant Energy				IPL				WPL
	March 31, 2017		December 31, 2016		March 31, 2017		December 31, 2016		March 31, 2017		December 31, 2016
Cost of removal obligations		$413.0		$411.6		$271.1		$269.4		$141.9		$142.2
Electric transmission cost recovery	128.3		72.0		75.9		35.7		52.4		36.3
IPL’s tax benefit riders	64.7		83.5		64.7		83.5		—		—
Commodity cost recovery	32.9		30.8		20.1		17.8		12.8		13.0
Energy efficiency cost recovery	20.6		20.5		—		—		20.6		20.5
Derivatives	9.0		31.5		5.1		12.1		3.9		19.4
Other	28.1		31.1		11.4		12.3		16.7		18.8
		$696.6		$681.0		$448.3		$430.8		$248.3		$250.2

Tax Benefit Riders

For the three months ended March 31, 2017, Alliant Energy’s and IPL’s “IPL’s tax benefit riders” regulatory liabilities decreased by $19 million as follows (in millions):

Electric tax benefit rider credits		$17
Gas tax benefit rider credits	2
		$19

WPL [Member]

Regulatory Assets [Line Items]

Regulatory Assets

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

	Alliant Energy				IPL				WPL
	March 31, 2017		December 31, 2016		March 31, 2017		December 31, 2016		March 31, 2017		December 31, 2016
Tax-related		$1,080.2		$1,055.6		$1,044.9		$1,022.4		$35.3		$33.2
Pension and OPEB costs	568.5		578.7		289.1		294.0		279.4		284.7
Asset retirement obligations	108.6		105.9		67.1		64.3		41.5		41.6
Derivatives	46.4		30.7		17.2		10.0		29.2		20.7
WPL’s EGUs retired early	39.7		41.4		—		—		39.7		41.4
Emission allowances	26.0		26.2		26.0		26.2		—		—
Other	93.6		76.6		56.5		41.9		37.1		34.7
		$1,963.0		$1,915.1		$1,500.8		$1,458.8		$462.2		$456.3

Regulatory Liabilities

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

	Alliant Energy				IPL				WPL
	March 31, 2017		December 31, 2016		March 31, 2017		December 31, 2016		March 31, 2017		December 31, 2016
Cost of removal obligations		$413.0		$411.6		$271.1		$269.4		$141.9		$142.2
Electric transmission cost recovery	128.3		72.0		75.9		35.7		52.4		36.3
IPL’s tax benefit riders	64.7		83.5		64.7		83.5		—		—
Commodity cost recovery	32.9		30.8		20.1		17.8		12.8		13.0
Energy efficiency cost recovery	20.6		20.5		—		—		20.6		20.5
Derivatives	9.0		31.5		5.1		12.1		3.9		19.4
Other	28.1		31.1		11.4		12.3		16.7		18.8
		$696.6		$681.0		$448.3		$430.8		$248.3		$250.2