Regulatory Matters (Tables)

6 Months Ended

Jun. 30, 2016

Regulatory Assets [Line Items]

Regulatory Assets

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

	Alliant Energy				IPL				WPL
	June 30, 2016		December 31, 2015		June 30, 2016		December 31, 2015		June 30, 2016		December 31, 2015
Tax-related		$1,020.1		$987.7		$988.1		$958.2		$32.0		$29.5
Pension and OPEB costs	560.5		579.5		289.2		298.1		271.3		281.4
AROs	99.7		92.4		57.7		50.8		42.0		41.6
WPL’s EGUs retired early	41.5		45.0		—		—		41.5		45.0
Derivatives	38.7		70.6		11.0		28.2		27.7		42.4
Emission allowances	26.6		26.9		26.6		26.9		—		—
Commodity cost recovery	19.8		35.9		0.3		2.8		19.5		33.1
Other	65.7		70.6		32.5		37.6		33.2		33.0
		$1,872.6		$1,908.6		$1,405.4		$1,402.6		$467.2		$506.0

Regulatory Liabilities

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

	Alliant Energy				IPL				WPL
	June 30, 2016		December 31, 2015		June 30, 2016		December 31, 2015		June 30, 2016		December 31, 2015
Cost of removal obligations		$408.8		$406.0		$264.8		$260.4		$144.0		$145.6
IPL’s tax benefit riders	123.1		159.2		123.1		159.2		—		—
Electric transmission cost recovery	59.5		43.5		31.7		21.9		27.8		21.6
Commodity cost recovery	41.9		37.6		20.5		23.5		21.4		14.1
Energy efficiency cost recovery	35.2		48.3		—		—		35.2		48.3
Other	42.8		43.1		23.3		24.2		19.5		18.9
		$711.3		$737.7		$463.4		$489.2		$247.9		$248.5

Tax Benefit Riders

For the six months ended June 30, 2016, Alliant Energy’s and IPL’s “IPL’s tax benefit riders” regulatory liabilities decreased by $36 million as follows (in millions):

Electric tax benefit rider credits		$30
Gas tax benefit rider credits	6
		$36

Customer Billing Credits

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

	Three Months			Six Months
	2016	2015		2016		2015
Billing credits to reduce retail electric customers’ bills	$2		$6		$4		$12

IPL [Member]

Regulatory Assets [Line Items]

Regulatory Assets

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

	Alliant Energy				IPL				WPL
	June 30, 2016		December 31, 2015		June 30, 2016		December 31, 2015		June 30, 2016		December 31, 2015
Tax-related		$1,020.1		$987.7		$988.1		$958.2		$32.0		$29.5
Pension and OPEB costs	560.5		579.5		289.2		298.1		271.3		281.4
AROs	99.7		92.4		57.7		50.8		42.0		41.6
WPL’s EGUs retired early	41.5		45.0		—		—		41.5		45.0
Derivatives	38.7		70.6		11.0		28.2		27.7		42.4
Emission allowances	26.6		26.9		26.6		26.9		—		—
Commodity cost recovery	19.8		35.9		0.3		2.8		19.5		33.1
Other	65.7		70.6		32.5		37.6		33.2		33.0
		$1,872.6		$1,908.6		$1,405.4		$1,402.6		$467.2		$506.0

Regulatory Liabilities

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

	Alliant Energy				IPL				WPL
	June 30, 2016		December 31, 2015		June 30, 2016		December 31, 2015		June 30, 2016		December 31, 2015
Cost of removal obligations		$408.8		$406.0		$264.8		$260.4		$144.0		$145.6
IPL’s tax benefit riders	123.1		159.2		123.1		159.2		—		—
Electric transmission cost recovery	59.5		43.5		31.7		21.9		27.8		21.6
Commodity cost recovery	41.9		37.6		20.5		23.5		21.4		14.1
Energy efficiency cost recovery	35.2		48.3		—		—		35.2		48.3
Other	42.8		43.1		23.3		24.2		19.5		18.9
		$711.3		$737.7		$463.4		$489.2		$247.9		$248.5

Tax Benefit Riders

For the six months ended June 30, 2016, Alliant Energy’s and IPL’s “IPL’s tax benefit riders” regulatory liabilities decreased by $36 million as follows (in millions):

Electric tax benefit rider credits		$30
Gas tax benefit rider credits	6
		$36

Customer Billing Credits

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

	Three Months			Six Months
	2016	2015		2016		2015
Billing credits to reduce retail electric customers’ bills	$2		$6		$4		$12

WPL [Member]

Regulatory Assets [Line Items]

Regulatory Assets

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

	Alliant Energy				IPL				WPL
	June 30, 2016		December 31, 2015		June 30, 2016		December 31, 2015		June 30, 2016		December 31, 2015
Tax-related		$1,020.1		$987.7		$988.1		$958.2		$32.0		$29.5
Pension and OPEB costs	560.5		579.5		289.2		298.1		271.3		281.4
AROs	99.7		92.4		57.7		50.8		42.0		41.6
WPL’s EGUs retired early	41.5		45.0		—		—		41.5		45.0
Derivatives	38.7		70.6		11.0		28.2		27.7		42.4
Emission allowances	26.6		26.9		26.6		26.9		—		—
Commodity cost recovery	19.8		35.9		0.3		2.8		19.5		33.1
Other	65.7		70.6		32.5		37.6		33.2		33.0
		$1,872.6		$1,908.6		$1,405.4		$1,402.6		$467.2		$506.0

Regulatory Liabilities

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

	Alliant Energy				IPL				WPL
	June 30, 2016		December 31, 2015		June 30, 2016		December 31, 2015		June 30, 2016		December 31, 2015
Cost of removal obligations		$408.8		$406.0		$264.8		$260.4		$144.0		$145.6
IPL’s tax benefit riders	123.1		159.2		123.1		159.2		—		—
Electric transmission cost recovery	59.5		43.5		31.7		21.9		27.8		21.6
Commodity cost recovery	41.9		37.6		20.5		23.5		21.4		14.1
Energy efficiency cost recovery	35.2		48.3		—		—		35.2		48.3
Other	42.8		43.1		23.3		24.2		19.5		18.9
		$711.3		$737.7		$463.4		$489.2		$247.9		$248.5