Regulatory Matters (Tables)

12 Months Ended

Dec. 31, 2016

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
	2016		2015		2016		2015		2016		2015
Tax-related		$1,055.6		$987.7		$1,022.4		$958.2		$33.2		$29.5
Pension and OPEB costs	578.7		579.5		294.0		298.1		284.7		281.4
AROs	105.9		92.4		64.3		50.8		41.6		41.6
WPL’s EGUs retired early	41.4		45.0		—		—		41.4		45.0
Derivatives	30.7		70.6		10.0		28.2		20.7		42.4
Emission allowances	26.2		26.9		26.2		26.9		—		—
Commodity cost recovery	6.0		35.9		0.3		2.8		5.7		33.1
Other	70.6		70.6		41.6		37.6		29.0		33.0
		$1,915.1		$1,908.6		$1,458.8		$1,402.6		$456.3		$506.0

Schedule of Regulatory Liabilities

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

	Alliant Energy				IPL				WPL
	2016		2015		2016		2015		2016		2015
Cost of removal obligations		$411.6		$406.0		$269.4		$260.4		$142.2		$145.6
IPL’s tax benefit riders	83.5		159.2		83.5		159.2		—		—
Electric transmission cost recovery	72.0		43.5		35.7		21.9		36.3		21.6
Derivatives	31.5		8.5		12.1		6.7		19.4		1.8
Commodity cost recovery	30.8		37.6		17.8		23.5		13.0		14.1
Energy efficiency cost recovery	20.5		48.3		—		—		20.5		48.3
Other	31.1		34.6		12.3		17.5		18.8		17.1
		$681.0		$737.7		$430.8		$489.2		$250.2		$248.5

Tax Benefit Riders

In 2016, Alliant Energy’s and IPL’s “IPL’s tax benefit riders” regulatory liabilities decreased by $76 million as follows (in millions):

Electric tax benefit rider credits		$64
Gas tax benefit rider credits	12
		$76

Electric Tax Benefit Rider

Details for IPL’s electric tax benefit rider are as follows (in millions):

	2016		2015		2014
Credit to IPL’s Iowa retail electric customers’ bills with reduction to electric revenues (based on customers’ KWh usage)		$64		$72		$85
Income tax benefit resulting from decreased taxable income caused by credits	27		30		35
Income tax benefit representing tax benefits realized from electric tax benefit rider	37		42		50

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):

	2016		2015		2014
Revenue requirement adjustment		$14		$14		$15

Gas Tax Benefit Rider

Details for IPL’s gas tax benefit rider are as follows (in millions):

	2016		2015		2014
Credit to IPL’s Iowa retail gas customers’ bills with reduction to gas revenues (based on a fixed amount per day)		$12		$12		$12
Income tax benefit resulting from decreased taxable income caused by credits	5		5		5
Income tax benefit representing tax benefits realized from gas tax benefit rider	7		7		7

Customer Billing Credits

The IUB approved a settlement agreement in 2014 related to rates charged to IPL’s Iowa retail electric customers. The settlement agreement extended IPL’s Iowa retail electric base rates authorized in its 2009 Test Year rate case through 2016 and provided targeted retail electric customer billing credits of $105 million in aggregate. IPL recorded such billing credits as follows (in millions):

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

Retail Fuel-related Rate Filings

Details on these rate increases, as well as amounts WPL deferred for the over-collected (included in “Commodity cost recovery” regulatory liabilities) or under-collected (included in “Commodity cost recovery” regulatory assets) fuel-related costs from its retail electric customers are as follows (dollars in millions):

	Retail Electric			Deferral of Over (Under)			Timing of Refunds To or
Year	Rate Increase			Collected Fuel-related Costs			Collections From Customers
2016		$7	1%		$9		Pending
2015	39		4%	10			2016
2014	19		2%	(28		)	2016

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
	2016		2015		2016		2015		2016		2015
Tax-related		$1,055.6		$987.7		$1,022.4		$958.2		$33.2		$29.5
Pension and OPEB costs	578.7		579.5		294.0		298.1		284.7		281.4
AROs	105.9		92.4		64.3		50.8		41.6		41.6
WPL’s EGUs retired early	41.4		45.0		—		—		41.4		45.0
Derivatives	30.7		70.6		10.0		28.2		20.7		42.4
Emission allowances	26.2		26.9		26.2		26.9		—		—
Commodity cost recovery	6.0		35.9		0.3		2.8		5.7		33.1
Other	70.6		70.6		41.6		37.6		29.0		33.0
		$1,915.1		$1,908.6		$1,458.8		$1,402.6		$456.3		$506.0

Schedule of Regulatory Liabilities

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

	Alliant Energy				IPL				WPL
	2016		2015		2016		2015		2016		2015
Cost of removal obligations		$411.6		$406.0		$269.4		$260.4		$142.2		$145.6
IPL’s tax benefit riders	83.5		159.2		83.5		159.2		—		—
Electric transmission cost recovery	72.0		43.5		35.7		21.9		36.3		21.6
Derivatives	31.5		8.5		12.1		6.7		19.4		1.8
Commodity cost recovery	30.8		37.6		17.8		23.5		13.0		14.1
Energy efficiency cost recovery	20.5		48.3		—		—		20.5		48.3
Other	31.1		34.6		12.3		17.5		18.8		17.1
		$681.0		$737.7		$430.8		$489.2		$250.2		$248.5

Tax Benefit Riders

In 2016, Alliant Energy’s and IPL’s “IPL’s tax benefit riders” regulatory liabilities decreased by $76 million as follows (in millions):

Electric tax benefit rider credits		$64
Gas tax benefit rider credits	12
		$76

Electric Tax Benefit Rider

Details for IPL’s electric tax benefit rider are as follows (in millions):

	2016		2015		2014
Credit to IPL’s Iowa retail electric customers’ bills with reduction to electric revenues (based on customers’ KWh usage)		$64		$72		$85
Income tax benefit resulting from decreased taxable income caused by credits	27		30		35
Income tax benefit representing tax benefits realized from electric tax benefit rider	37		42		50

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):

	2016		2015		2014
Revenue requirement adjustment		$14		$14		$15

Gas Tax Benefit Rider

Details for IPL’s gas tax benefit rider are as follows (in millions):

	2016		2015		2014
Credit to IPL’s Iowa retail gas customers’ bills with reduction to gas revenues (based on a fixed amount per day)		$12		$12		$12
Income tax benefit resulting from decreased taxable income caused by credits	5		5		5
Income tax benefit representing tax benefits realized from gas tax benefit rider	7		7		7

Customer Billing Credits

The IUB approved a settlement agreement in 2014 related to rates charged to IPL’s Iowa retail electric customers. The settlement agreement extended IPL’s Iowa retail electric base rates authorized in its 2009 Test Year rate case through 2016 and provided targeted retail electric customer billing credits of $105 million in aggregate. IPL recorded such billing credits as follows (in millions):

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

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
	2016		2015		2016		2015		2016		2015
Tax-related		$1,055.6		$987.7		$1,022.4		$958.2		$33.2		$29.5
Pension and OPEB costs	578.7		579.5		294.0		298.1		284.7		281.4
AROs	105.9		92.4		64.3		50.8		41.6		41.6
WPL’s EGUs retired early	41.4		45.0		—		—		41.4		45.0
Derivatives	30.7		70.6		10.0		28.2		20.7		42.4
Emission allowances	26.2		26.9		26.2		26.9		—		—
Commodity cost recovery	6.0		35.9		0.3		2.8		5.7		33.1
Other	70.6		70.6		41.6		37.6		29.0		33.0
		$1,915.1		$1,908.6		$1,458.8		$1,402.6		$456.3		$506.0

Schedule of Regulatory Liabilities

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

	Alliant Energy				IPL				WPL
	2016		2015		2016		2015		2016		2015
Cost of removal obligations		$411.6		$406.0		$269.4		$260.4		$142.2		$145.6
IPL’s tax benefit riders	83.5		159.2		83.5		159.2		—		—
Electric transmission cost recovery	72.0		43.5		35.7		21.9		36.3		21.6
Derivatives	31.5		8.5		12.1		6.7		19.4		1.8
Commodity cost recovery	30.8		37.6		17.8		23.5		13.0		14.1
Energy efficiency cost recovery	20.5		48.3		—		—		20.5		48.3
Other	31.1		34.6		12.3		17.5		18.8		17.1
		$681.0		$737.7		$430.8		$489.2		$250.2		$248.5

Retail Fuel-related Rate Filings

Details on these rate increases, as well as amounts WPL deferred for the over-collected (included in “Commodity cost recovery” regulatory liabilities) or under-collected (included in “Commodity cost recovery” regulatory assets) fuel-related costs from its retail electric customers are as follows (dollars in millions):

	Retail Electric			Deferral of Over (Under)			Timing of Refunds To or
Year	Rate Increase			Collected Fuel-related Costs			Collections From Customers
2016		$7	1%		$9		Pending
2015	39		4%	10			2016
2014	19		2%	(28		)	2016