Regulatory Matters (Tables)

12 Months Ended

Dec. 31, 2015

Regulatory Assets [Line Items]

Schedule of Regulatory Assets

At December 31, regulatory assets were comprised of the following items (in millions):

	Alliant Energy				IPL				WPL
	2015		2014		2015		2014		2015		2014
Tax-related		$987.7		$955.3		$958.2		$928.0		$29.5		$27.3
Pension and OPEB costs	579.5		570.2		298.1		287.9		281.4		282.3
AROs	92.4		73.7		50.8		41.4		41.6		32.3
Derivatives	70.6		46.9		28.2		28.0		42.4		18.9
WPL’s EGUs retired early	45.0		—		—		—		45.0		—
Commodity cost recovery	35.9		31.1		2.8		0.4		33.1		30.7
Emission allowances	26.9		27.4		26.9		27.4		—		—
Environmental-related costs	16.4		16.0		11.0		11.5		5.4		4.5
Debt redemption costs	14.3		16.1		9.5		10.9		4.8		5.2
Other	39.9		47.0		17.1		22.4		22.8		24.6
		$1,908.6		$1,783.7		$1,402.6		$1,357.9		$506.0		$425.8

Schedule of Regulatory Liabilities

At December 31, regulatory liabilities were comprised of the following items (in millions):

	Alliant Energy				IPL				WPL
	2015		2014		2015		2014		2015		2014
Cost of removal obligations		$406.0		$421.7		$260.4		$279.1		$145.6		$142.6
IPL’s tax benefit riders	159.2		243.0		159.2		243.0		—		—
Energy efficiency cost recovery	48.3		64.3		—		—		48.3		64.3
Electric transmission cost recovery	43.5		19.4		21.9		19.4		21.6		—
Commodity cost recovery	37.6		15.4		23.5		15.1		14.1		0.3
Other	43.1		57.4		24.2		26.9		18.9		30.5
		$737.7		$821.2		$489.2		$583.5		$248.5		$237.7

Tax Benefit Riders

In 2015, Alliant Energy’s and IPL’s “IPL’s tax benefit riders” regulatory liabilities decreased by $84 million as follows (in millions):

Electric tax benefit rider credits		$72
Gas tax benefit rider credits	12
		$84

Electric Tax Benefit Rider

Alliant Energy and IPL recognize an offsetting reduction to income tax expense for the after-tax amounts credited to IPL’s retail electric customers’ bills in Iowa, resulting in no impact to Alliant Energy’s and IPL’s net income from the electric tax benefit rider as follows (in millions):

	2015		2014		2013
Credit to IPL’s Iowa retail electric customers’ bills with reduction to electric revenues		$72		$85		$79
Income tax benefit resulting from decreased taxable income caused by credits	30		35		33
Income tax benefit representing tax benefits realized from electric tax benefit rider	42		50		46

Revenue Requirement Adjustment

The revenue requirement adjustment resulted in increases to electric revenues in Alliant Energy’s and IPL’s income statements and was recognized through the energy adjustment clause as a reduction of the credits on IPL’s Iowa retail electric customers’ bills from the electric tax benefit rider as follows (in millions):

	2015		2014		2013
Revenue requirement adjustment		$14		$15		$24

Gas Tax Benefit Rider

Alliant Energy and IPL utilized gas tax benefit rider-related regulatory liabilities to credit IPL’s Iowa retail gas customers’ bills as follows (in millions):

	2015		2014		2013
Credit to IPL’s Iowa retail gas customers’ bills with reduction to gas revenues		$12		$12		$11
Income tax benefit resulting from decreased taxable income caused by credits	5		5		4
Income tax benefit representing tax benefits realized from gas tax benefit rider	7		7		7

Customer Billing Credits

IPL recorded such billing credits in 2014 and 2015, and estimates billing credits in 2016, as follows (in millions):

	Actual				Estimated
	2014		2015		2016
Billing credits to reduce retail electric customers’ bills		$72		$24		$9

IPL [Member]

Regulatory Assets [Line Items]

Schedule of Regulatory Assets

At December 31, regulatory assets were comprised of the following items (in millions):

	Alliant Energy				IPL				WPL
	2015		2014		2015		2014		2015		2014
Tax-related		$987.7		$955.3		$958.2		$928.0		$29.5		$27.3
Pension and OPEB costs	579.5		570.2		298.1		287.9		281.4		282.3
AROs	92.4		73.7		50.8		41.4		41.6		32.3
Derivatives	70.6		46.9		28.2		28.0		42.4		18.9
WPL’s EGUs retired early	45.0		—		—		—		45.0		—
Commodity cost recovery	35.9		31.1		2.8		0.4		33.1		30.7
Emission allowances	26.9		27.4		26.9		27.4		—		—
Environmental-related costs	16.4		16.0		11.0		11.5		5.4		4.5
Debt redemption costs	14.3		16.1		9.5		10.9		4.8		5.2
Other	39.9		47.0		17.1		22.4		22.8		24.6
		$1,908.6		$1,783.7		$1,402.6		$1,357.9		$506.0		$425.8

Schedule of Regulatory Liabilities

At December 31, regulatory liabilities were comprised of the following items (in millions):

	Alliant Energy				IPL				WPL
	2015		2014		2015		2014		2015		2014
Cost of removal obligations		$406.0		$421.7		$260.4		$279.1		$145.6		$142.6
IPL’s tax benefit riders	159.2		243.0		159.2		243.0		—		—
Energy efficiency cost recovery	48.3		64.3		—		—		48.3		64.3
Electric transmission cost recovery	43.5		19.4		21.9		19.4		21.6		—
Commodity cost recovery	37.6		15.4		23.5		15.1		14.1		0.3
Other	43.1		57.4		24.2		26.9		18.9		30.5
		$737.7		$821.2		$489.2		$583.5		$248.5		$237.7

Tax Benefit Riders

In 2015, Alliant Energy’s and IPL’s “IPL’s tax benefit riders” regulatory liabilities decreased by $84 million as follows (in millions):

Electric tax benefit rider credits		$72
Gas tax benefit rider credits	12
		$84

Electric Tax Benefit Rider

Alliant Energy and IPL recognize an offsetting reduction to income tax expense for the after-tax amounts credited to IPL’s retail electric customers’ bills in Iowa, resulting in no impact to Alliant Energy’s and IPL’s net income from the electric tax benefit rider as follows (in millions):

	2015		2014		2013
Credit to IPL’s Iowa retail electric customers’ bills with reduction to electric revenues		$72		$85		$79
Income tax benefit resulting from decreased taxable income caused by credits	30		35		33
Income tax benefit representing tax benefits realized from electric tax benefit rider	42		50		46

Revenue Requirement Adjustment

The revenue requirement adjustment resulted in increases to electric revenues in Alliant Energy’s and IPL’s income statements and was recognized through the energy adjustment clause as a reduction of the credits on IPL’s Iowa retail electric customers’ bills from the electric tax benefit rider as follows (in millions):

	2015		2014		2013
Revenue requirement adjustment		$14		$15		$24

Gas Tax Benefit Rider

Alliant Energy and IPL utilized gas tax benefit rider-related regulatory liabilities to credit IPL’s Iowa retail gas customers’ bills as follows (in millions):

	2015		2014		2013
Credit to IPL’s Iowa retail gas customers’ bills with reduction to gas revenues		$12		$12		$11
Income tax benefit resulting from decreased taxable income caused by credits	5		5		4
Income tax benefit representing tax benefits realized from gas tax benefit rider	7		7		7

Customer Billing Credits

IPL recorded such billing credits in 2014 and 2015, and estimates billing credits in 2016, as follows (in millions):

	Actual				Estimated
	2014		2015		2016
Billing credits to reduce retail electric customers’ bills		$72		$24		$9

WPL [Member]

Regulatory Assets [Line Items]

Schedule of Regulatory Assets

At December 31, regulatory assets were comprised of the following items (in millions):

	Alliant Energy				IPL				WPL
	2015		2014		2015		2014		2015		2014
Tax-related		$987.7		$955.3		$958.2		$928.0		$29.5		$27.3
Pension and OPEB costs	579.5		570.2		298.1		287.9		281.4		282.3
AROs	92.4		73.7		50.8		41.4		41.6		32.3
Derivatives	70.6		46.9		28.2		28.0		42.4		18.9
WPL’s EGUs retired early	45.0		—		—		—		45.0		—
Commodity cost recovery	35.9		31.1		2.8		0.4		33.1		30.7
Emission allowances	26.9		27.4		26.9		27.4		—		—
Environmental-related costs	16.4		16.0		11.0		11.5		5.4		4.5
Debt redemption costs	14.3		16.1		9.5		10.9		4.8		5.2
Other	39.9		47.0		17.1		22.4		22.8		24.6
		$1,908.6		$1,783.7		$1,402.6		$1,357.9		$506.0		$425.8

Schedule of Regulatory Liabilities

At December 31, regulatory liabilities were comprised of the following items (in millions):

	Alliant Energy				IPL				WPL
	2015		2014		2015		2014		2015		2014
Cost of removal obligations		$406.0		$421.7		$260.4		$279.1		$145.6		$142.6
IPL’s tax benefit riders	159.2		243.0		159.2		243.0		—		—
Energy efficiency cost recovery	48.3		64.3		—		—		48.3		64.3
Electric transmission cost recovery	43.5		19.4		21.9		19.4		21.6		—
Commodity cost recovery	37.6		15.4		23.5		15.1		14.1		0.3
Other	43.1		57.4		24.2		26.9		18.9		30.5
		$737.7		$821.2		$489.2		$583.5		$248.5		$237.7