Regulatory Matters (Tables)

9 Months Ended

Sep. 30, 2015

Regulatory Assets [Line Items]

Regulatory Assets

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

	Alliant Energy				IPL				WPL
	September 30, 2015		December 31, 2014		September 30, 2015		December 31, 2014		September 30, 2015		December 31, 2014
Tax-related		$976.5		$955.3		$947.3		$928.0		$29.2		$27.3
Pension and OPEB costs	548.4		570.2		278.6		287.9		269.8		282.3
AROs	81.8		73.7		47.6		41.4		34.2		32.3
Derivatives	68.4		46.9		29.3		28.0		39.1		18.9
Commodity cost recovery	33.2		31.1		1.2		0.4		32.0		30.7
Emission allowances	26.5		27.4		26.5		27.4		—		—
Other	73.1		79.1		39.7		44.8		33.4		34.3
		$1,807.9		$1,783.7		$1,370.2		$1,357.9		$437.7		$425.8

Regulatory Liabilities

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

	Alliant Energy				IPL				WPL
	September 30, 2015		December 31, 2014		September 30, 2015		December 31, 2014		September 30, 2015		December 31, 2014
Cost of removal obligations		$406.2		$421.7		$261.3		$279.1		$144.9		$142.6
IPL’s tax benefit riders	179.5		243.0		179.5		243.0		—		—
Energy efficiency cost recovery	53.0		64.3		—		—		53.0		64.3
Commodity cost recovery	33.8		15.4		22.9		15.1		10.9		0.3
Electric transmission cost recovery	31.4		19.4		15.8		19.4		15.6		—
Other	40.2		57.4		23.0		26.9		17.2		30.5
		$744.1		$821.2		$502.5		$583.5		$241.6		$237.7

Tax Benefit Riders

For the nine months ended September 30, 2015, Alliant Energy’s and IPL’s “IPL’s tax benefit riders” regulatory liabilities decreased by $64 million as follows (in millions):

Electric tax benefit rider credits		$55
Gas tax benefit rider credits	9
		$64

Customer Billing Credits

For the three and nine months ended September 30, IPL recorded billing credits to reduce retail electric customers’ bills as follows (in millions):

	Three Months			Nine Months
	2015	2014		2015		2014
Billing credits to reduce retail electric customers’ bills	$7		$26		$19		$46

IPL [Member]

Regulatory Assets [Line Items]

Regulatory Assets

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

	Alliant Energy				IPL				WPL
	September 30, 2015		December 31, 2014		September 30, 2015		December 31, 2014		September 30, 2015		December 31, 2014
Tax-related		$976.5		$955.3		$947.3		$928.0		$29.2		$27.3
Pension and OPEB costs	548.4		570.2		278.6		287.9		269.8		282.3
AROs	81.8		73.7		47.6		41.4		34.2		32.3
Derivatives	68.4		46.9		29.3		28.0		39.1		18.9
Commodity cost recovery	33.2		31.1		1.2		0.4		32.0		30.7
Emission allowances	26.5		27.4		26.5		27.4		—		—
Other	73.1		79.1		39.7		44.8		33.4		34.3
		$1,807.9		$1,783.7		$1,370.2		$1,357.9		$437.7		$425.8

Regulatory Liabilities

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

	Alliant Energy				IPL				WPL
	September 30, 2015		December 31, 2014		September 30, 2015		December 31, 2014		September 30, 2015		December 31, 2014
Cost of removal obligations		$406.2		$421.7		$261.3		$279.1		$144.9		$142.6
IPL’s tax benefit riders	179.5		243.0		179.5		243.0		—		—
Energy efficiency cost recovery	53.0		64.3		—		—		53.0		64.3
Commodity cost recovery	33.8		15.4		22.9		15.1		10.9		0.3
Electric transmission cost recovery	31.4		19.4		15.8		19.4		15.6		—
Other	40.2		57.4		23.0		26.9		17.2		30.5
		$744.1		$821.2		$502.5		$583.5		$241.6		$237.7

Tax Benefit Riders

For the nine months ended September 30, 2015, Alliant Energy’s and IPL’s “IPL’s tax benefit riders” regulatory liabilities decreased by $64 million as follows (in millions):

Electric tax benefit rider credits		$55
Gas tax benefit rider credits	9
		$64

Customer Billing Credits

For the three and nine months ended September 30, IPL recorded billing credits to reduce retail electric customers’ bills as follows (in millions):

	Three Months			Nine Months
	2015	2014		2015		2014
Billing credits to reduce retail electric customers’ bills	$7		$26		$19		$46

WPL [Member]

Regulatory Assets [Line Items]

Regulatory Assets

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

	Alliant Energy				IPL				WPL
	September 30, 2015		December 31, 2014		September 30, 2015		December 31, 2014		September 30, 2015		December 31, 2014
Tax-related		$976.5		$955.3		$947.3		$928.0		$29.2		$27.3
Pension and OPEB costs	548.4		570.2		278.6		287.9		269.8		282.3
AROs	81.8		73.7		47.6		41.4		34.2		32.3
Derivatives	68.4		46.9		29.3		28.0		39.1		18.9
Commodity cost recovery	33.2		31.1		1.2		0.4		32.0		30.7
Emission allowances	26.5		27.4		26.5		27.4		—		—
Other	73.1		79.1		39.7		44.8		33.4		34.3
		$1,807.9		$1,783.7		$1,370.2		$1,357.9		$437.7		$425.8

Regulatory Liabilities

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

	Alliant Energy				IPL				WPL
	September 30, 2015		December 31, 2014		September 30, 2015		December 31, 2014		September 30, 2015		December 31, 2014
Cost of removal obligations		$406.2		$421.7		$261.3		$279.1		$144.9		$142.6
IPL’s tax benefit riders	179.5		243.0		179.5		243.0		—		—
Energy efficiency cost recovery	53.0		64.3		—		—		53.0		64.3
Commodity cost recovery	33.8		15.4		22.9		15.1		10.9		0.3
Electric transmission cost recovery	31.4		19.4		15.8		19.4		15.6		—
Other	40.2		57.4		23.0		26.9		17.2		30.5
		$744.1		$821.2		$502.5		$583.5		$241.6		$237.7