Regulatory Matters (Tables)

3 Months Ended

Mar. 31, 2015

Regulatory Assets [Line Items]

Regulatory Assets

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

	Alliant Energy				IPL				WPL
	March 31, 2015		December 31, 2014		March 31, 2015		December 31, 2014		March 31, 2015		December 31, 2014
Tax-related		$968.2		$955.3		$940.5		$928.0		$27.7		$27.3
Pension and OPEB costs	562.9		570.2		284.8		287.9		278.1		282.3
AROs	75.6		73.7		42.5		41.4		33.1		32.3
Derivatives	49.6		46.9		26.4		28.0		23.2		18.9
Commodity cost recovery	32.1		31.1		0.6		0.4		31.5		30.7
Emission allowances	26.9		27.4		26.9		27.4		—		—
Other	75.0		79.1		42.0		44.8		33.0		34.3
		$1,790.3		$1,783.7		$1,363.7		$1,357.9		$426.6		$425.8

Regulatory Liabilities

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

	Alliant Energy				IPL				WPL
	March 31, 2015		December 31, 2014		March 31, 2015		December 31, 2014		March 31, 2015		December 31, 2014
Cost of removal obligations		$423.2		$421.7		$279.5		$279.1		$143.7		$142.6
IPL’s tax benefit riders	222.0		243.0		222.0		243.0		—		—
Energy efficiency cost recovery	62.2		64.3		1.6		—		60.6		64.3
Commodity cost recovery	26.5		15.4		22.8		15.1		3.7		0.3
IPL’s electric transmission cost recovery	23.2		19.4		23.2		19.4		—		—
Other	59.0		57.4		23.0		26.9		36.0		30.5
		$816.1		$821.2		$572.1		$583.5		$244.0		$237.7

Tax Benefit Riders

For the three months ended March 31, 2015, Alliant Energy’s and IPL’s “IPL’s tax benefit riders” regulatory liabilities decreased by $21 million as follows (in millions):

Electric tax benefit rider credits		$18
Gas tax benefit rider credits	3
		$21

Customer Billing Credits

For the three months ended March 31, IPL recorded billing credits to reduce retail electric customers’ bills as follows (in millions):

	2015
Billing credits to reduce retail electric customers’ bills	$6

IPL [Member]

Regulatory Assets [Line Items]

Regulatory Assets

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

	Alliant Energy				IPL				WPL
	March 31, 2015		December 31, 2014		March 31, 2015		December 31, 2014		March 31, 2015		December 31, 2014
Tax-related		$968.2		$955.3		$940.5		$928.0		$27.7		$27.3
Pension and OPEB costs	562.9		570.2		284.8		287.9		278.1		282.3
AROs	75.6		73.7		42.5		41.4		33.1		32.3
Derivatives	49.6		46.9		26.4		28.0		23.2		18.9
Commodity cost recovery	32.1		31.1		0.6		0.4		31.5		30.7
Emission allowances	26.9		27.4		26.9		27.4		—		—
Other	75.0		79.1		42.0		44.8		33.0		34.3
		$1,790.3		$1,783.7		$1,363.7		$1,357.9		$426.6		$425.8

Regulatory Liabilities

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

	Alliant Energy				IPL				WPL
	March 31, 2015		December 31, 2014		March 31, 2015		December 31, 2014		March 31, 2015		December 31, 2014
Cost of removal obligations		$423.2		$421.7		$279.5		$279.1		$143.7		$142.6
IPL’s tax benefit riders	222.0		243.0		222.0		243.0		—		—
Energy efficiency cost recovery	62.2		64.3		1.6		—		60.6		64.3
Commodity cost recovery	26.5		15.4		22.8		15.1		3.7		0.3
IPL’s electric transmission cost recovery	23.2		19.4		23.2		19.4		—		—
Other	59.0		57.4		23.0		26.9		36.0		30.5
		$816.1		$821.2		$572.1		$583.5		$244.0		$237.7

Tax Benefit Riders

For the three months ended March 31, 2015, Alliant Energy’s and IPL’s “IPL’s tax benefit riders” regulatory liabilities decreased by $21 million as follows (in millions):

Electric tax benefit rider credits		$18
Gas tax benefit rider credits	3
		$21

Customer Billing Credits

For the three months ended March 31, IPL recorded billing credits to reduce retail electric customers’ bills as follows (in millions):

	2015
Billing credits to reduce retail electric customers’ bills	$6

WPL [Member]

Regulatory Assets [Line Items]

Regulatory Assets

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

	Alliant Energy				IPL				WPL
	March 31, 2015		December 31, 2014		March 31, 2015		December 31, 2014		March 31, 2015		December 31, 2014
Tax-related		$968.2		$955.3		$940.5		$928.0		$27.7		$27.3
Pension and OPEB costs	562.9		570.2		284.8		287.9		278.1		282.3
AROs	75.6		73.7		42.5		41.4		33.1		32.3
Derivatives	49.6		46.9		26.4		28.0		23.2		18.9
Commodity cost recovery	32.1		31.1		0.6		0.4		31.5		30.7
Emission allowances	26.9		27.4		26.9		27.4		—		—
Other	75.0		79.1		42.0		44.8		33.0		34.3
		$1,790.3		$1,783.7		$1,363.7		$1,357.9		$426.6		$425.8

Regulatory Liabilities

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

	Alliant Energy				IPL				WPL
	March 31, 2015		December 31, 2014		March 31, 2015		December 31, 2014		March 31, 2015		December 31, 2014
Cost of removal obligations		$423.2		$421.7		$279.5		$279.1		$143.7		$142.6
IPL’s tax benefit riders	222.0		243.0		222.0		243.0		—		—
Energy efficiency cost recovery	62.2		64.3		1.6		—		60.6		64.3
Commodity cost recovery	26.5		15.4		22.8		15.1		3.7		0.3
IPL’s electric transmission cost recovery	23.2		19.4		23.2		19.4		—		—
Other	59.0		57.4		23.0		26.9		36.0		30.5
		$816.1		$821.2		$572.1		$583.5		$244.0		$237.7