Regulatory Matters (Tables)

3 Months Ended

Mar. 31, 2016

Regulatory Assets [Line Items]

Regulatory Assets

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

	Alliant Energy				IPL				WPL
	March 31, 2016		December 31, 2015		March 31, 2016		December 31, 2015		March 31, 2016		December 31, 2015
Tax-related		$1,002.7		$987.7		$972.0		$958.2		$30.7		$29.5
Pension and OPEB costs	570.0		579.5		293.6		298.1		276.4		281.4
AROs	96.1		92.4		54.1		50.8		42.0		41.6
Derivatives	86.6		70.6		25.5		28.2		61.1		42.4
WPL’s EGUs retired early	43.2		45.0		—		—		43.2		45.0
Emission allowances	26.7		26.9		26.7		26.9		—		—
Commodity cost recovery	26.3		35.9		0.3		2.8		26.0		33.1
Other	65.6		70.6		33.7		37.6		31.9		33.0
		$1,917.2		$1,908.6		$1,405.9		$1,402.6		$511.3		$506.0

Regulatory Liabilities

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

	Alliant Energy				IPL				WPL
	March 31, 2016		December 31, 2015		March 31, 2016		December 31, 2015		March 31, 2016		December 31, 2015
Cost of removal obligations		$408.1		$406.0		$263.1		$260.4		$145.0		$145.6
IPL’s tax benefit riders	141.1		159.2		141.1		159.2		—		—
Electric transmission cost recovery	51.4		43.5		25.5		21.9		25.9		21.6
Energy efficiency cost recovery	41.6		48.3		—		—		41.6		48.3
Commodity cost recovery	35.2		37.6		20.4		23.5		14.8		14.1
Other	33.6		43.1		18.1		24.2		15.5		18.9
		$711.0		$737.7		$468.2		$489.2		$242.8		$248.5

Tax Benefit Riders

For the three months ended March 31, 2016, Alliant Energy’s and IPL’s “IPL’s tax benefit riders” regulatory liabilities decreased by $18 million as follows (in millions):

Electric tax benefit rider credits		$15
Gas tax benefit rider credits	3
		$18

Customer Billing Credits

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

	2016	2015
Billing credits to reduce retail electric customers’ bills	$2		$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, 2016		December 31, 2015		March 31, 2016		December 31, 2015		March 31, 2016		December 31, 2015
Tax-related		$1,002.7		$987.7		$972.0		$958.2		$30.7		$29.5
Pension and OPEB costs	570.0		579.5		293.6		298.1		276.4		281.4
AROs	96.1		92.4		54.1		50.8		42.0		41.6
Derivatives	86.6		70.6		25.5		28.2		61.1		42.4
WPL’s EGUs retired early	43.2		45.0		—		—		43.2		45.0
Emission allowances	26.7		26.9		26.7		26.9		—		—
Commodity cost recovery	26.3		35.9		0.3		2.8		26.0		33.1
Other	65.6		70.6		33.7		37.6		31.9		33.0
		$1,917.2		$1,908.6		$1,405.9		$1,402.6		$511.3		$506.0

Regulatory Liabilities

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

	Alliant Energy				IPL				WPL
	March 31, 2016		December 31, 2015		March 31, 2016		December 31, 2015		March 31, 2016		December 31, 2015
Cost of removal obligations		$408.1		$406.0		$263.1		$260.4		$145.0		$145.6
IPL’s tax benefit riders	141.1		159.2		141.1		159.2		—		—
Electric transmission cost recovery	51.4		43.5		25.5		21.9		25.9		21.6
Energy efficiency cost recovery	41.6		48.3		—		—		41.6		48.3
Commodity cost recovery	35.2		37.6		20.4		23.5		14.8		14.1
Other	33.6		43.1		18.1		24.2		15.5		18.9
		$711.0		$737.7		$468.2		$489.2		$242.8		$248.5

Tax Benefit Riders

For the three months ended March 31, 2016, Alliant Energy’s and IPL’s “IPL’s tax benefit riders” regulatory liabilities decreased by $18 million as follows (in millions):

Electric tax benefit rider credits		$15
Gas tax benefit rider credits	3
		$18

Customer Billing Credits

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

	2016	2015
Billing credits to reduce retail electric customers’ bills	$2		$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, 2016		December 31, 2015		March 31, 2016		December 31, 2015		March 31, 2016		December 31, 2015
Tax-related		$1,002.7		$987.7		$972.0		$958.2		$30.7		$29.5
Pension and OPEB costs	570.0		579.5		293.6		298.1		276.4		281.4
AROs	96.1		92.4		54.1		50.8		42.0		41.6
Derivatives	86.6		70.6		25.5		28.2		61.1		42.4
WPL’s EGUs retired early	43.2		45.0		—		—		43.2		45.0
Emission allowances	26.7		26.9		26.7		26.9		—		—
Commodity cost recovery	26.3		35.9		0.3		2.8		26.0		33.1
Other	65.6		70.6		33.7		37.6		31.9		33.0
		$1,917.2		$1,908.6		$1,405.9		$1,402.6		$511.3		$506.0

Regulatory Liabilities

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

	Alliant Energy				IPL				WPL
	March 31, 2016		December 31, 2015		March 31, 2016		December 31, 2015		March 31, 2016		December 31, 2015
Cost of removal obligations		$408.1		$406.0		$263.1		$260.4		$145.0		$145.6
IPL’s tax benefit riders	141.1		159.2		141.1		159.2		—		—
Electric transmission cost recovery	51.4		43.5		25.5		21.9		25.9		21.6
Energy efficiency cost recovery	41.6		48.3		—		—		41.6		48.3
Commodity cost recovery	35.2		37.6		20.4		23.5		14.8		14.1
Other	33.6		43.1		18.1		24.2		15.5		18.9
		$711.0		$737.7		$468.2		$489.2		$242.8		$248.5