Regulatory Matters (Tables)

3 Months Ended

Mar. 31, 2014

Regulatory Assets [Line Items]

Regulatory Assets

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

	Alliant Energy				IPL				WPL
	March 31, 2014		December 31, 2013		March 31, 2014		December 31, 2013		March 31, 2014		December 31, 2013
Tax-related		$834.0		$829.7		$808.3		$798.6		$25.7		$31.1
Pension and OPEB costs	351.8		355.3		172.6		174.2		179.2		181.1
AROs	68.5		65.7		38.6		36.7		29.9		29.0
Environmental-related costs	27.8		25.0		23.0		21.0		4.8		4.0
Emission allowances	29.2		30.0		29.2		30.0		—		—
Derivatives	9.1		21.1		2.5		5.9		6.6		15.2
Other	96.9		86.4		43.8		47.1		53.1		39.3
		$1,417.3		$1,413.2		$1,118.0		$1,113.5		$299.3		$299.7

Regulatory Liabilities

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

	Alliant Energy				IPL				WPL
	March 31, 2014		December 31, 2013		March 31, 2014		December 31, 2013		March 31, 2014		December 31, 2013
Cost of removal obligations		$420.0		$418.9		$279.3		$277.7		$140.7		$141.2
IPL’s tax benefit riders	239.8		265.4		239.8		265.4		—		—
Energy efficiency cost recovery	64.1		52.7		14.9		9.3		49.2		43.4
Derivatives	33.3		7.2		8.8		3.6		24.5		3.6
IPL’s electric transmission cost recovery	21.2		14.6		21.2		14.6		—		—
IPL’s electric transmission assets sale	18.8		21.6		18.8		21.6		—		—
Other	39.2		41.1		21.2		22.7		18.0		18.4
		$836.4		$821.5		$604.0		$614.9		$232.4		$206.6

Tax Benefit Riders

For the three months ended March 31, 2014, Alliant Energy and IPL utilized “IPL’s tax benefit riders” regulatory liabilities to credit IPL’s Iowa retail electric and gas customers’ bills as follows (in millions):

Electric tax benefit rider		$23
Gas tax benefit rider	3
		$26

IPL [Member]

Regulatory Assets [Line Items]

Regulatory Assets

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

	Alliant Energy				IPL				WPL
	March 31, 2014		December 31, 2013		March 31, 2014		December 31, 2013		March 31, 2014		December 31, 2013
Tax-related		$834.0		$829.7		$808.3		$798.6		$25.7		$31.1
Pension and OPEB costs	351.8		355.3		172.6		174.2		179.2		181.1
AROs	68.5		65.7		38.6		36.7		29.9		29.0
Environmental-related costs	27.8		25.0		23.0		21.0		4.8		4.0
Emission allowances	29.2		30.0		29.2		30.0		—		—
Derivatives	9.1		21.1		2.5		5.9		6.6		15.2
Other	96.9		86.4		43.8		47.1		53.1		39.3
		$1,417.3		$1,413.2		$1,118.0		$1,113.5		$299.3		$299.7

Regulatory Liabilities

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

	Alliant Energy				IPL				WPL
	March 31, 2014		December 31, 2013		March 31, 2014		December 31, 2013		March 31, 2014		December 31, 2013
Cost of removal obligations		$420.0		$418.9		$279.3		$277.7		$140.7		$141.2
IPL’s tax benefit riders	239.8		265.4		239.8		265.4		—		—
Energy efficiency cost recovery	64.1		52.7		14.9		9.3		49.2		43.4
Derivatives	33.3		7.2		8.8		3.6		24.5		3.6
IPL’s electric transmission cost recovery	21.2		14.6		21.2		14.6		—		—
IPL’s electric transmission assets sale	18.8		21.6		18.8		21.6		—		—
Other	39.2		41.1		21.2		22.7		18.0		18.4
		$836.4		$821.5		$604.0		$614.9		$232.4		$206.6

Tax Benefit Riders

For the three months ended March 31, 2014, Alliant Energy and IPL utilized “IPL’s tax benefit riders” regulatory liabilities to credit IPL’s Iowa retail electric and gas customers’ bills as follows (in millions):

Electric tax benefit rider		$23
Gas tax benefit rider	3
		$26

WPL [Member]

Regulatory Assets [Line Items]

Regulatory Assets

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

	Alliant Energy				IPL				WPL
	March 31, 2014		December 31, 2013		March 31, 2014		December 31, 2013		March 31, 2014		December 31, 2013
Tax-related		$834.0		$829.7		$808.3		$798.6		$25.7		$31.1
Pension and OPEB costs	351.8		355.3		172.6		174.2		179.2		181.1
AROs	68.5		65.7		38.6		36.7		29.9		29.0
Environmental-related costs	27.8		25.0		23.0		21.0		4.8		4.0
Emission allowances	29.2		30.0		29.2		30.0		—		—
Derivatives	9.1		21.1		2.5		5.9		6.6		15.2
Other	96.9		86.4		43.8		47.1		53.1		39.3
		$1,417.3		$1,413.2		$1,118.0		$1,113.5		$299.3		$299.7

Regulatory Liabilities

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

	Alliant Energy				IPL				WPL
	March 31, 2014		December 31, 2013		March 31, 2014		December 31, 2013		March 31, 2014		December 31, 2013
Cost of removal obligations		$420.0		$418.9		$279.3		$277.7		$140.7		$141.2
IPL’s tax benefit riders	239.8		265.4		239.8		265.4		—		—
Energy efficiency cost recovery	64.1		52.7		14.9		9.3		49.2		43.4
Derivatives	33.3		7.2		8.8		3.6		24.5		3.6
IPL’s electric transmission cost recovery	21.2		14.6		21.2		14.6		—		—
IPL’s electric transmission assets sale	18.8		21.6		18.8		21.6		—		—
Other	39.2		41.1		21.2		22.7		18.0		18.4
		$836.4		$821.5		$604.0		$614.9		$232.4		$206.6