Income Taxes (Tables)

12 Months Ended

Dec. 31, 2017

Income Tax [Line Items]

Schedule Of Impacts Of the Tax Cuts And Jobs Act of 2017

Alliant Energy, IPL and WPL have completed their assessment of the applicable provisions of Tax Reform, and the impacts to their 2017 balance sheets and income statements are as follows (in millions):

	Alliant Energy			IPL			WPL
Balance Sheet
Other current assets		$—			$4.7			($1.4	)
Investments:
ATC Investment	(75.0		)	—			—
Other assets:
Regulatory assets	(387.6		)	(375.0		)	(12.7		)
Deferred charges and other	41.0			—			—
Total Tax Reform impact on assets		($421.6	)		($370.3	)		($14.1	)
Other liabilities:
Deferred tax liabilities		($1,331.9	)		($757.2	)		($523.8	)
Regulatory liabilities	885.9			390.7			495.2
Other	6.3			—			—
Total Tax Reform impact on liabilities		($439.7	)		($366.5	)		($28.6	)
Income Statement
Income tax expense (benefit)		($18.1	)		$3.8			($14.5	)

Schedule of Components of Income Tax Expense (Benefit)

The components of “Income tax expense (benefit)” in the income statements were as follows (in millions):

	Alliant Energy									IPL									WPL
	2017			2016			2015			2017			2016			2015			2017			2016			2015
Current tax expense (benefit):
Federal		($41.0	)		$1.8			$2.0			($27.9	)		($12.8	)		($14.1	)		$5.5			($22.3	)		$4.7
State	8.5			17.2			3.2			1.6			15.5			11.5			2.5			1.1			0.6
IPL’s tax benefit riders	(40.4		)	(44.2		)	(49.0		)	(40.4		)	(44.2		)	(49.0		)	—			—			—
Deferred tax expense (benefit):
Federal	159.5			112.8			120.8			72.5			59.1			40.7			55.0			112.3			76.8
State	12.3			4.9			27.9			(2.2		)	(9.0		)	3.3			16.6			20.8			20.2
Production tax credits	(31.1		)	(31.8		)	(33.1		)	(14.1		)	(14.0		)	(14.5		)	(17.0		)	(17.8		)	(18.6		)
Investment tax credits	(1.1		)	(1.3		)	(1.4		)	(0.4		)	(0.5		)	(0.6		)	(0.7		)	(0.8		)	(0.8		)
		$66.7			$59.4			$70.4			($10.9	)		($5.9	)		($22.7	)		$61.9			$93.3			$82.9

Schedule Of Effective Income Tax Rates

The overall income tax rates shown in the following table were computed by dividing income tax expense (benefit) by income from continuing operations before income taxes.

	Alliant Energy						IPL						WPL
	2017		2016		2015		2017		2016		2015		2017		2016		2015
Statutory federal income tax rate	35.0	%	35.0	%	35.0	%	35.0	%	35.0	%	35.0	%	35.0	%	35.0	%	35.0	%
State income taxes, net of federal benefits	5.5		5.4		5.2		6.5		6.4		6.2		5.1		5.1		5.1
Effect of rate-making on property-related differences	(8.5	)	(8.5	)	(6.8	)	(19.1	)	(16.2	)	(17.2	)	(1.7	)	(0.7	)	(0.5	)
IPL’s tax benefit riders	(7.6	)	(10.0	)	(10.6	)	(18.7	)	(20.1	)	(28.3	)	—		—		—
Production tax credits	(6.1	)	(7.2	)	(7.2	)	(6.7	)	(6.3	)	(8.3	)	(7.1	)	(6.2	)	(7.1	)
Impact of Tax Reform	(3.4	)	—		—		1.7		—		—		(5.8	)	—		—
Other items, net	(2.4	)	(1.3	)	(0.3	)	(3.7	)	(1.5	)	(0.5	)	(0.6	)	(0.6	)	(0.7	)
Overall income tax rate	12.5	%	13.4	%	15.3	%	(5.0	%)	(2.7	%)	(13.1	%)	24.9	%	32.6	%	31.8	%

Schedule of Deferred Tax Assets and Liabilities

The deferred tax assets and liabilities included on the balance sheets at December 31 arise from the following temporary differences (in millions):

	Alliant Energy						IPL					WPL
	2017			2016			2017			2016		2017			2016
Deferred tax liabilities:
Property		$1,852.7			$2,919.0			$1,102.6			$1,677.0		$674.2			$1,124.5
ATC Investment	86.4			153.1			—			—		—			—
Other	75.9			95.1			63.4			71.4		36.5			58.8
Total deferred tax liabilities	2,015.0			3,167.2			1,166.0			1,748.4		710.7			1,183.3
Deferred tax assets:
Federal credit carryforwards	260.7			268.4			113.1			95.9		131.0			112.9
Net operating losses carryforwards - federal	174.4			173.3			107.4			69.6		43.7			75.4
Regulatory liability - IPL’s tax benefit riders	7.4			34.7			7.4			34.7		—			—
Net operating losses carryforwards - state	41.3			32.9			0.9			0.6		0.2			0.1
Other	61.8			87.9			27.1			35.8		14.7			23.6
Subtotal deferred tax assets	545.6			597.2			255.9			236.6		189.6			212.0
Valuation allowance	(9.0		)	(0.2		)	(0.6		)	—		(1.3		)	(0.3		)
Total deferred tax assets	536.6			597.0			255.3			236.6		188.3			211.7
Total deferred tax liabilities, net		$1,478.4			$2,570.2			$910.7			$1,511.8		$522.4			$971.6

Summary Of Tax Credit Carryforwards

At December 31, 2017, carryforwards and expiration dates were estimated as follows (in millions):

	Range of Expiration Dates	Alliant Energy		IPL		WPL
Federal net operating losses	2030-2037		$852		$537		$208
State net operating losses	2018-2037	700		13		2
Federal tax credits	2022-2037	267		119		131

Schedule Of Open Tax Years

Tax years that remain subject to the statute of limitations in the major jurisdictions for each of Alliant Energy, IPL and WPL are as follows:

Consolidated federal income tax returns (a)	2014	-	2016
Consolidated Iowa income tax returns (b)	2014	-	2016
Wisconsin combined tax returns (c)	2013	-	2016

(a) These federal tax returns are effectively settled as a result of participation in the IRS Compliance Assurance Program, which allows Alliant Energy and the IRS to work together to resolve issues related to Alliant Energy’s current tax year before filing its federal income tax return. The statute of limitations for these federal tax returns expires three years from each filing date.

(b) The statute of limitations for these Iowa tax returns expires three years from each filing date.

(c) The statute of limitations for these Wisconsin combined tax returns expires four years from each filing date.

IPL [Member]

Income Tax [Line Items]

Schedule Of Impacts Of the Tax Cuts And Jobs Act of 2017

Alliant Energy, IPL and WPL have completed their assessment of the applicable provisions of Tax Reform, and the impacts to their 2017 balance sheets and income statements are as follows (in millions):

	Alliant Energy			IPL			WPL
Balance Sheet
Other current assets		$—			$4.7			($1.4	)
Investments:
ATC Investment	(75.0		)	—			—
Other assets:
Regulatory assets	(387.6		)	(375.0		)	(12.7		)
Deferred charges and other	41.0			—			—
Total Tax Reform impact on assets		($421.6	)		($370.3	)		($14.1	)
Other liabilities:
Deferred tax liabilities		($1,331.9	)		($757.2	)		($523.8	)
Regulatory liabilities	885.9			390.7			495.2
Other	6.3			—			—
Total Tax Reform impact on liabilities		($439.7	)		($366.5	)		($28.6	)
Income Statement
Income tax expense (benefit)		($18.1	)		$3.8			($14.5	)

Schedule of Components of Income Tax Expense (Benefit)

The components of “Income tax expense (benefit)” in the income statements were as follows (in millions):

	Alliant Energy									IPL									WPL
	2017			2016			2015			2017			2016			2015			2017			2016			2015
Current tax expense (benefit):
Federal		($41.0	)		$1.8			$2.0			($27.9	)		($12.8	)		($14.1	)		$5.5			($22.3	)		$4.7
State	8.5			17.2			3.2			1.6			15.5			11.5			2.5			1.1			0.6
IPL’s tax benefit riders	(40.4		)	(44.2		)	(49.0		)	(40.4		)	(44.2		)	(49.0		)	—			—			—
Deferred tax expense (benefit):
Federal	159.5			112.8			120.8			72.5			59.1			40.7			55.0			112.3			76.8
State	12.3			4.9			27.9			(2.2		)	(9.0		)	3.3			16.6			20.8			20.2
Production tax credits	(31.1		)	(31.8		)	(33.1		)	(14.1		)	(14.0		)	(14.5		)	(17.0		)	(17.8		)	(18.6		)
Investment tax credits	(1.1		)	(1.3		)	(1.4		)	(0.4		)	(0.5		)	(0.6		)	(0.7		)	(0.8		)	(0.8		)
		$66.7			$59.4			$70.4			($10.9	)		($5.9	)		($22.7	)		$61.9			$93.3			$82.9

Schedule Of Effective Income Tax Rates

The overall income tax rates shown in the following table were computed by dividing income tax expense (benefit) by income from continuing operations before income taxes.

	Alliant Energy						IPL						WPL
	2017		2016		2015		2017		2016		2015		2017		2016		2015
Statutory federal income tax rate	35.0	%	35.0	%	35.0	%	35.0	%	35.0	%	35.0	%	35.0	%	35.0	%	35.0	%
State income taxes, net of federal benefits	5.5		5.4		5.2		6.5		6.4		6.2		5.1		5.1		5.1
Effect of rate-making on property-related differences	(8.5	)	(8.5	)	(6.8	)	(19.1	)	(16.2	)	(17.2	)	(1.7	)	(0.7	)	(0.5	)
IPL’s tax benefit riders	(7.6	)	(10.0	)	(10.6	)	(18.7	)	(20.1	)	(28.3	)	—		—		—
Production tax credits	(6.1	)	(7.2	)	(7.2	)	(6.7	)	(6.3	)	(8.3	)	(7.1	)	(6.2	)	(7.1	)
Impact of Tax Reform	(3.4	)	—		—		1.7		—		—		(5.8	)	—		—
Other items, net	(2.4	)	(1.3	)	(0.3	)	(3.7	)	(1.5	)	(0.5	)	(0.6	)	(0.6	)	(0.7	)
Overall income tax rate	12.5	%	13.4	%	15.3	%	(5.0	%)	(2.7	%)	(13.1	%)	24.9	%	32.6	%	31.8	%

Schedule of Deferred Tax Assets and Liabilities

The deferred tax assets and liabilities included on the balance sheets at December 31 arise from the following temporary differences (in millions):

	Alliant Energy						IPL					WPL
	2017			2016			2017			2016		2017			2016
Deferred tax liabilities:
Property		$1,852.7			$2,919.0			$1,102.6			$1,677.0		$674.2			$1,124.5
ATC Investment	86.4			153.1			—			—		—			—
Other	75.9			95.1			63.4			71.4		36.5			58.8
Total deferred tax liabilities	2,015.0			3,167.2			1,166.0			1,748.4		710.7			1,183.3
Deferred tax assets:
Federal credit carryforwards	260.7			268.4			113.1			95.9		131.0			112.9
Net operating losses carryforwards - federal	174.4			173.3			107.4			69.6		43.7			75.4
Regulatory liability - IPL’s tax benefit riders	7.4			34.7			7.4			34.7		—			—
Net operating losses carryforwards - state	41.3			32.9			0.9			0.6		0.2			0.1
Other	61.8			87.9			27.1			35.8		14.7			23.6
Subtotal deferred tax assets	545.6			597.2			255.9			236.6		189.6			212.0
Valuation allowance	(9.0		)	(0.2		)	(0.6		)	—		(1.3		)	(0.3		)
Total deferred tax assets	536.6			597.0			255.3			236.6		188.3			211.7
Total deferred tax liabilities, net		$1,478.4			$2,570.2			$910.7			$1,511.8		$522.4			$971.6

Summary Of Tax Credit Carryforwards

At December 31, 2017, carryforwards and expiration dates were estimated as follows (in millions):

	Range of Expiration Dates	Alliant Energy		IPL		WPL
Federal net operating losses	2030-2037		$852		$537		$208
State net operating losses	2018-2037	700		13		2
Federal tax credits	2022-2037	267		119		131

Schedule Of Open Tax Years

Tax years that remain subject to the statute of limitations in the major jurisdictions for each of Alliant Energy, IPL and WPL are as follows:

Consolidated federal income tax returns (a)	2014	-	2016
Consolidated Iowa income tax returns (b)	2014	-	2016
Wisconsin combined tax returns (c)	2013	-	2016

(a) These federal tax returns are effectively settled as a result of participation in the IRS Compliance Assurance Program, which allows Alliant Energy and the IRS to work together to resolve issues related to Alliant Energy’s current tax year before filing its federal income tax return. The statute of limitations for these federal tax returns expires three years from each filing date.

(b) The statute of limitations for these Iowa tax returns expires three years from each filing date.

(c) The statute of limitations for these Wisconsin combined tax returns expires four years from each filing date.

WPL [Member]

Income Tax [Line Items]

Schedule Of Impacts Of the Tax Cuts And Jobs Act of 2017

Alliant Energy, IPL and WPL have completed their assessment of the applicable provisions of Tax Reform, and the impacts to their 2017 balance sheets and income statements are as follows (in millions):

	Alliant Energy			IPL			WPL
Balance Sheet
Other current assets		$—			$4.7			($1.4	)
Investments:
ATC Investment	(75.0		)	—			—
Other assets:
Regulatory assets	(387.6		)	(375.0		)	(12.7		)
Deferred charges and other	41.0			—			—
Total Tax Reform impact on assets		($421.6	)		($370.3	)		($14.1	)
Other liabilities:
Deferred tax liabilities		($1,331.9	)		($757.2	)		($523.8	)
Regulatory liabilities	885.9			390.7			495.2
Other	6.3			—			—
Total Tax Reform impact on liabilities		($439.7	)		($366.5	)		($28.6	)
Income Statement
Income tax expense (benefit)		($18.1	)		$3.8			($14.5	)

Schedule of Components of Income Tax Expense (Benefit)

The components of “Income tax expense (benefit)” in the income statements were as follows (in millions):

	Alliant Energy									IPL									WPL
	2017			2016			2015			2017			2016			2015			2017			2016			2015
Current tax expense (benefit):
Federal		($41.0	)		$1.8			$2.0			($27.9	)		($12.8	)		($14.1	)		$5.5			($22.3	)		$4.7
State	8.5			17.2			3.2			1.6			15.5			11.5			2.5			1.1			0.6
IPL’s tax benefit riders	(40.4		)	(44.2		)	(49.0		)	(40.4		)	(44.2		)	(49.0		)	—			—			—
Deferred tax expense (benefit):
Federal	159.5			112.8			120.8			72.5			59.1			40.7			55.0			112.3			76.8
State	12.3			4.9			27.9			(2.2		)	(9.0		)	3.3			16.6			20.8			20.2
Production tax credits	(31.1		)	(31.8		)	(33.1		)	(14.1		)	(14.0		)	(14.5		)	(17.0		)	(17.8		)	(18.6		)
Investment tax credits	(1.1		)	(1.3		)	(1.4		)	(0.4		)	(0.5		)	(0.6		)	(0.7		)	(0.8		)	(0.8		)
		$66.7			$59.4			$70.4			($10.9	)		($5.9	)		($22.7	)		$61.9			$93.3			$82.9

Schedule Of Effective Income Tax Rates

The overall income tax rates shown in the following table were computed by dividing income tax expense (benefit) by income from continuing operations before income taxes.

	Alliant Energy						IPL						WPL
	2017		2016		2015		2017		2016		2015		2017		2016		2015
Statutory federal income tax rate	35.0	%	35.0	%	35.0	%	35.0	%	35.0	%	35.0	%	35.0	%	35.0	%	35.0	%
State income taxes, net of federal benefits	5.5		5.4		5.2		6.5		6.4		6.2		5.1		5.1		5.1
Effect of rate-making on property-related differences	(8.5	)	(8.5	)	(6.8	)	(19.1	)	(16.2	)	(17.2	)	(1.7	)	(0.7	)	(0.5	)
IPL’s tax benefit riders	(7.6	)	(10.0	)	(10.6	)	(18.7	)	(20.1	)	(28.3	)	—		—		—
Production tax credits	(6.1	)	(7.2	)	(7.2	)	(6.7	)	(6.3	)	(8.3	)	(7.1	)	(6.2	)	(7.1	)
Impact of Tax Reform	(3.4	)	—		—		1.7		—		—		(5.8	)	—		—
Other items, net	(2.4	)	(1.3	)	(0.3	)	(3.7	)	(1.5	)	(0.5	)	(0.6	)	(0.6	)	(0.7	)
Overall income tax rate	12.5	%	13.4	%	15.3	%	(5.0	%)	(2.7	%)	(13.1	%)	24.9	%	32.6	%	31.8	%

Schedule of Deferred Tax Assets and Liabilities

The deferred tax assets and liabilities included on the balance sheets at December 31 arise from the following temporary differences (in millions):

	Alliant Energy						IPL					WPL
	2017			2016			2017			2016		2017			2016
Deferred tax liabilities:
Property		$1,852.7			$2,919.0			$1,102.6			$1,677.0		$674.2			$1,124.5
ATC Investment	86.4			153.1			—			—		—			—
Other	75.9			95.1			63.4			71.4		36.5			58.8
Total deferred tax liabilities	2,015.0			3,167.2			1,166.0			1,748.4		710.7			1,183.3
Deferred tax assets:
Federal credit carryforwards	260.7			268.4			113.1			95.9		131.0			112.9
Net operating losses carryforwards - federal	174.4			173.3			107.4			69.6		43.7			75.4
Regulatory liability - IPL’s tax benefit riders	7.4			34.7			7.4			34.7		—			—
Net operating losses carryforwards - state	41.3			32.9			0.9			0.6		0.2			0.1
Other	61.8			87.9			27.1			35.8		14.7			23.6
Subtotal deferred tax assets	545.6			597.2			255.9			236.6		189.6			212.0
Valuation allowance	(9.0		)	(0.2		)	(0.6		)	—		(1.3		)	(0.3		)
Total deferred tax assets	536.6			597.0			255.3			236.6		188.3			211.7
Total deferred tax liabilities, net		$1,478.4			$2,570.2			$910.7			$1,511.8		$522.4			$971.6

Summary Of Tax Credit Carryforwards

At December 31, 2017, carryforwards and expiration dates were estimated as follows (in millions):

	Range of Expiration Dates	Alliant Energy		IPL		WPL
Federal net operating losses	2030-2037		$852		$537		$208
State net operating losses	2018-2037	700		13		2
Federal tax credits	2022-2037	267		119		131

Schedule Of Open Tax Years

Tax years that remain subject to the statute of limitations in the major jurisdictions for each of Alliant Energy, IPL and WPL are as follows:

Consolidated federal income tax returns (a)	2014	-	2016
Consolidated Iowa income tax returns (b)	2014	-	2016
Wisconsin combined tax returns (c)	2013	-	2016

(a) These federal tax returns are effectively settled as a result of participation in the IRS Compliance Assurance Program, which allows Alliant Energy and the IRS to work together to resolve issues related to Alliant Energy’s current tax year before filing its federal income tax return. The statute of limitations for these federal tax returns expires three years from each filing date.

(b) The statute of limitations for these Iowa tax returns expires three years from each filing date.

(c) The statute of limitations for these Wisconsin combined tax returns expires four years from each filing date.