Regulatory Matters (Tables)

6 Months Ended

Jun. 30, 2015

Regulatory Assets [Line Items]

Regulatory Assets

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

	Alliant Energy				IPL				WPL
	June 30, 2015		December 31, 2014		June 30, 2015		December 31, 2014		June 30, 2015		December 31, 2014
Tax-related		$961.1		$955.3		$932.8		$928.0		$28.3		$27.3
Pension and OPEB costs	555.7		570.2		281.8		287.9		273.9		282.3
AROs	77.9		73.7		44.1		41.4		33.8		32.3
Derivatives	54.1		46.9		26.1		28.0		28.0		18.9
Commodity cost recovery	32.3		31.1		0.5		0.4		31.8		30.7
Emission allowances	26.7		27.4		26.7		27.4		—		—
Other	70.1		79.1		38.7		44.8		31.4		34.3
		$1,777.9		$1,783.7		$1,350.7		$1,357.9		$427.2		$425.8

Regulatory Liabilities

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

	Alliant Energy				IPL				WPL
	June 30, 2015		December 31, 2014		June 30, 2015		December 31, 2014		June 30, 2015		December 31, 2014
Cost of removal obligations		$410.6		$421.7		$266.6		$279.1		$144.0		$142.6
IPL’s tax benefit riders	201.9		243.0		201.9		243.0		—		—
Energy efficiency cost recovery	58.5		64.3		1.7		—		56.8		64.3
IPL’s electric transmission cost recovery	24.3		19.4		24.3		19.4		—		—
Commodity cost recovery	16.6		15.4		11.6		15.1		5.0		0.3
Other	58.2		57.4		25.9		26.9		32.3		30.5
		$770.1		$821.2		$532.0		$583.5		$238.1		$237.7

Tax Benefit Riders

For the six months ended June 30, 2015, Alliant Energy’s and IPL’s “IPL’s tax benefit riders” regulatory liabilities decreased by $41 million as follows (in millions):

Electric tax benefit rider credits		$35
Gas tax benefit rider credits	6
		$41

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
	2015	2014		2015		2014
Billing credits to reduce retail electric customers’ bills	$6		$20		$12		$20

IPL [Member]

Regulatory Assets [Line Items]

Regulatory Assets

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

	Alliant Energy				IPL				WPL
	June 30, 2015		December 31, 2014		June 30, 2015		December 31, 2014		June 30, 2015		December 31, 2014
Tax-related		$961.1		$955.3		$932.8		$928.0		$28.3		$27.3
Pension and OPEB costs	555.7		570.2		281.8		287.9		273.9		282.3
AROs	77.9		73.7		44.1		41.4		33.8		32.3
Derivatives	54.1		46.9		26.1		28.0		28.0		18.9
Commodity cost recovery	32.3		31.1		0.5		0.4		31.8		30.7
Emission allowances	26.7		27.4		26.7		27.4		—		—
Other	70.1		79.1		38.7		44.8		31.4		34.3
		$1,777.9		$1,783.7		$1,350.7		$1,357.9		$427.2		$425.8

Regulatory Liabilities

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

	Alliant Energy				IPL				WPL
	June 30, 2015		December 31, 2014		June 30, 2015		December 31, 2014		June 30, 2015		December 31, 2014
Cost of removal obligations		$410.6		$421.7		$266.6		$279.1		$144.0		$142.6
IPL’s tax benefit riders	201.9		243.0		201.9		243.0		—		—
Energy efficiency cost recovery	58.5		64.3		1.7		—		56.8		64.3
IPL’s electric transmission cost recovery	24.3		19.4		24.3		19.4		—		—
Commodity cost recovery	16.6		15.4		11.6		15.1		5.0		0.3
Other	58.2		57.4		25.9		26.9		32.3		30.5
		$770.1		$821.2		$532.0		$583.5		$238.1		$237.7

Tax Benefit Riders

For the six months ended June 30, 2015, Alliant Energy’s and IPL’s “IPL’s tax benefit riders” regulatory liabilities decreased by $41 million as follows (in millions):

Electric tax benefit rider credits		$35
Gas tax benefit rider credits	6
		$41

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
	2015	2014		2015		2014
Billing credits to reduce retail electric customers’ bills	$6		$20		$12		$20

WPL [Member]

Regulatory Assets [Line Items]

Regulatory Assets

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

	Alliant Energy				IPL				WPL
	June 30, 2015		December 31, 2014		June 30, 2015		December 31, 2014		June 30, 2015		December 31, 2014
Tax-related		$961.1		$955.3		$932.8		$928.0		$28.3		$27.3
Pension and OPEB costs	555.7		570.2		281.8		287.9		273.9		282.3
AROs	77.9		73.7		44.1		41.4		33.8		32.3
Derivatives	54.1		46.9		26.1		28.0		28.0		18.9
Commodity cost recovery	32.3		31.1		0.5		0.4		31.8		30.7
Emission allowances	26.7		27.4		26.7		27.4		—		—
Other	70.1		79.1		38.7		44.8		31.4		34.3
		$1,777.9		$1,783.7		$1,350.7		$1,357.9		$427.2		$425.8

Regulatory Liabilities

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

	Alliant Energy				IPL				WPL
	June 30, 2015		December 31, 2014		June 30, 2015		December 31, 2014		June 30, 2015		December 31, 2014
Cost of removal obligations		$410.6		$421.7		$266.6		$279.1		$144.0		$142.6
IPL’s tax benefit riders	201.9		243.0		201.9		243.0		—		—
Energy efficiency cost recovery	58.5		64.3		1.7		—		56.8		64.3
IPL’s electric transmission cost recovery	24.3		19.4		24.3		19.4		—		—
Commodity cost recovery	16.6		15.4		11.6		15.1		5.0		0.3
Other	58.2		57.4		25.9		26.9		32.3		30.5
		$770.1		$821.2		$532.0		$583.5		$238.1		$237.7