Income Taxes (Tables)

12 Months Ended

Dec. 31, 2016

Income Tax [Line Items]

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
	2016			2015			2014			2016			2015			2014			2016			2015			2014
Current tax expense (benefit):
Federal		$1.8			$2.0			$36.6			($12.8	)		($14.1	)		$8.9			($22.3	)		$4.7			$2.0
State	17.2			3.2			9.3			15.5			11.5			10.4			1.1			0.6			0.8
IPL’s tax benefit riders	(44.2		)	(49.0		)	(56.7		)	(44.2		)	(49.0		)	(56.7		)	—			—			—
Deferred tax expense (benefit):
Federal	112.8			120.8			83.5			59.1			40.7			10.8			112.3			76.8			81.1
State	4.9			27.9			4.6			(9.0		)	3.3			(7.9		)	20.8			20.2			20.0
Production tax credits	(31.8		)	(33.1		)	(31.3		)	(14.0		)	(14.5		)	(13.8		)	(17.8		)	(18.6		)	(17.5		)
Investment tax credits	(1.3		)	(1.4		)	(1.6		)	(0.5		)	(0.6		)	(0.6		)	(0.8		)	(0.8		)	(1.0		)
Provision recorded as a change in accrued interest	—			—			(0.1		)	—			—			—			—			—			(0.1		)
		$59.4			$70.4			$44.3			($5.9	)		($22.7	)		($48.9	)		$93.3			$82.9			$85.3

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
	2016		2015		2014		2016		2015		2014		2016		2015		2014
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	5.4		5.2		5.4		6.4		6.2		6.1		5.1		5.1		5.1
IPL’s tax benefit riders	(10.0	)	(10.6	)	(12.9	)	(20.1	)	(28.3	)	(39.6	)	—		—		—
Effect of rate-making on property-related differences	(8.5	)	(6.8	)	(7.5	)	(16.2	)	(17.2	)	(21.9	)	(0.7	)	(0.5	)	(0.7	)
Production tax credits	(7.2	)	(7.2	)	(7.1	)	(6.3	)	(8.3	)	(9.6	)	(6.2	)	(7.1	)	(6.6	)
Adjustment of prior period taxes	(0.8	)	0.8		(1.3	)	(1.2	)	0.7		(3.0	)	(0.1	)	0.1		—
Other items, net	(0.5	)	(1.1	)	(1.5	)	(0.3	)	(1.2	)	(1.2	)	(0.5	)	(0.8	)	(0.8	)
Overall income tax rate	13.4	%	15.3	%	10.1	%	(2.7	%)	(13.1	%)	(34.2	%)	32.6	%	31.8	%	32.0	%

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
	2016		2015		2016		2015		2016		2015
Deferred tax liabilities:
Property		$2,919.0		$2,762.9		$1,677.0		$1,587.8		$1,124.5		$1,027.0
Investment in ATC	153.1		138.1		—		—		—		138.9
Other	95.3		157.3		71.4		87.8		59.1		67.9
Total deferred tax liabilities	3,167.4		3,058.3		1,748.4		1,675.6		1,183.6		1,233.8
Deferred tax assets:
Federal credit carryforwards	268.4		236.4		95.9		81.7		112.9		95.5
Net operating losses carryforwards - federal	173.3		250.9		69.6		113.1		75.4		105.1
Regulatory liability - IPL’s tax benefit riders	34.7		66.1		34.7		66.1		—		—
Net operating losses carryforwards - state	32.9		38.3		0.6		1.1		0.1		3.6
Other	87.9		85.4		35.8		35.6		23.6		24.2
Total deferred tax assets	597.2		677.1		236.6		297.6		212.0		228.4
Total deferred tax liabilities, net		$2,570.2		$2,381.2		$1,511.8		$1,378.0		$971.6		$1,005.4

Summary Of Tax Credit Carryforwards

At December 31, 2016, carryforwards and expiration dates were estimated as follows (in millions):

	Range of Expiration Dates	Alliant Energy		IPL		WPL
Federal net operating losses	2030-2034		$506		$206		$215
State net operating losses	2018-2034	673		12		2
Federal tax credits	2022-2036	274		100		113

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)	2013	-	2015
Consolidated Iowa income tax returns (b)	2013	-	2015
Wisconsin combined tax returns (c)	2012	-	2015

(a) The federal tax returns for 2013 and 2014 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 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
	2016			2015			2014			2016			2015			2014			2016			2015			2014
Current tax expense (benefit):
Federal		$1.8			$2.0			$36.6			($12.8	)		($14.1	)		$8.9			($22.3	)		$4.7			$2.0
State	17.2			3.2			9.3			15.5			11.5			10.4			1.1			0.6			0.8
IPL’s tax benefit riders	(44.2		)	(49.0		)	(56.7		)	(44.2		)	(49.0		)	(56.7		)	—			—			—
Deferred tax expense (benefit):
Federal	112.8			120.8			83.5			59.1			40.7			10.8			112.3			76.8			81.1
State	4.9			27.9			4.6			(9.0		)	3.3			(7.9		)	20.8			20.2			20.0
Production tax credits	(31.8		)	(33.1		)	(31.3		)	(14.0		)	(14.5		)	(13.8		)	(17.8		)	(18.6		)	(17.5		)
Investment tax credits	(1.3		)	(1.4		)	(1.6		)	(0.5		)	(0.6		)	(0.6		)	(0.8		)	(0.8		)	(1.0		)
Provision recorded as a change in accrued interest	—			—			(0.1		)	—			—			—			—			—			(0.1		)
		$59.4			$70.4			$44.3			($5.9	)		($22.7	)		($48.9	)		$93.3			$82.9			$85.3

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
	2016		2015		2014		2016		2015		2014		2016		2015		2014
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	5.4		5.2		5.4		6.4		6.2		6.1		5.1		5.1		5.1
IPL’s tax benefit riders	(10.0	)	(10.6	)	(12.9	)	(20.1	)	(28.3	)	(39.6	)	—		—		—
Effect of rate-making on property-related differences	(8.5	)	(6.8	)	(7.5	)	(16.2	)	(17.2	)	(21.9	)	(0.7	)	(0.5	)	(0.7	)
Production tax credits	(7.2	)	(7.2	)	(7.1	)	(6.3	)	(8.3	)	(9.6	)	(6.2	)	(7.1	)	(6.6	)
Adjustment of prior period taxes	(0.8	)	0.8		(1.3	)	(1.2	)	0.7		(3.0	)	(0.1	)	0.1		—
Other items, net	(0.5	)	(1.1	)	(1.5	)	(0.3	)	(1.2	)	(1.2	)	(0.5	)	(0.8	)	(0.8	)
Overall income tax rate	13.4	%	15.3	%	10.1	%	(2.7	%)	(13.1	%)	(34.2	%)	32.6	%	31.8	%	32.0	%

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
	2016		2015		2016		2015		2016		2015
Deferred tax liabilities:
Property		$2,919.0		$2,762.9		$1,677.0		$1,587.8		$1,124.5		$1,027.0
Investment in ATC	153.1		138.1		—		—		—		138.9
Other	95.3		157.3		71.4		87.8		59.1		67.9
Total deferred tax liabilities	3,167.4		3,058.3		1,748.4		1,675.6		1,183.6		1,233.8
Deferred tax assets:
Federal credit carryforwards	268.4		236.4		95.9		81.7		112.9		95.5
Net operating losses carryforwards - federal	173.3		250.9		69.6		113.1		75.4		105.1
Regulatory liability - IPL’s tax benefit riders	34.7		66.1		34.7		66.1		—		—
Net operating losses carryforwards - state	32.9		38.3		0.6		1.1		0.1		3.6
Other	87.9		85.4		35.8		35.6		23.6		24.2
Total deferred tax assets	597.2		677.1		236.6		297.6		212.0		228.4
Total deferred tax liabilities, net		$2,570.2		$2,381.2		$1,511.8		$1,378.0		$971.6		$1,005.4

Summary Of Tax Credit Carryforwards

At December 31, 2016, carryforwards and expiration dates were estimated as follows (in millions):

	Range of Expiration Dates	Alliant Energy		IPL		WPL
Federal net operating losses	2030-2034		$506		$206		$215
State net operating losses	2018-2034	673		12		2
Federal tax credits	2022-2036	274		100		113

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)	2013	-	2015
Consolidated Iowa income tax returns (b)	2013	-	2015
Wisconsin combined tax returns (c)	2012	-	2015

(a) The federal tax returns for 2013 and 2014 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 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
	2016			2015			2014			2016			2015			2014			2016			2015			2014
Current tax expense (benefit):
Federal		$1.8			$2.0			$36.6			($12.8	)		($14.1	)		$8.9			($22.3	)		$4.7			$2.0
State	17.2			3.2			9.3			15.5			11.5			10.4			1.1			0.6			0.8
IPL’s tax benefit riders	(44.2		)	(49.0		)	(56.7		)	(44.2		)	(49.0		)	(56.7		)	—			—			—
Deferred tax expense (benefit):
Federal	112.8			120.8			83.5			59.1			40.7			10.8			112.3			76.8			81.1
State	4.9			27.9			4.6			(9.0		)	3.3			(7.9		)	20.8			20.2			20.0
Production tax credits	(31.8		)	(33.1		)	(31.3		)	(14.0		)	(14.5		)	(13.8		)	(17.8		)	(18.6		)	(17.5		)
Investment tax credits	(1.3		)	(1.4		)	(1.6		)	(0.5		)	(0.6		)	(0.6		)	(0.8		)	(0.8		)	(1.0		)
Provision recorded as a change in accrued interest	—			—			(0.1		)	—			—			—			—			—			(0.1		)
		$59.4			$70.4			$44.3			($5.9	)		($22.7	)		($48.9	)		$93.3			$82.9			$85.3

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
	2016		2015		2014		2016		2015		2014		2016		2015		2014
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	5.4		5.2		5.4		6.4		6.2		6.1		5.1		5.1		5.1
IPL’s tax benefit riders	(10.0	)	(10.6	)	(12.9	)	(20.1	)	(28.3	)	(39.6	)	—		—		—
Effect of rate-making on property-related differences	(8.5	)	(6.8	)	(7.5	)	(16.2	)	(17.2	)	(21.9	)	(0.7	)	(0.5	)	(0.7	)
Production tax credits	(7.2	)	(7.2	)	(7.1	)	(6.3	)	(8.3	)	(9.6	)	(6.2	)	(7.1	)	(6.6	)
Adjustment of prior period taxes	(0.8	)	0.8		(1.3	)	(1.2	)	0.7		(3.0	)	(0.1	)	0.1		—
Other items, net	(0.5	)	(1.1	)	(1.5	)	(0.3	)	(1.2	)	(1.2	)	(0.5	)	(0.8	)	(0.8	)
Overall income tax rate	13.4	%	15.3	%	10.1	%	(2.7	%)	(13.1	%)	(34.2	%)	32.6	%	31.8	%	32.0	%

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
	2016		2015		2016		2015		2016		2015
Deferred tax liabilities:
Property		$2,919.0		$2,762.9		$1,677.0		$1,587.8		$1,124.5		$1,027.0
Investment in ATC	153.1		138.1		—		—		—		138.9
Other	95.3		157.3		71.4		87.8		59.1		67.9
Total deferred tax liabilities	3,167.4		3,058.3		1,748.4		1,675.6		1,183.6		1,233.8
Deferred tax assets:
Federal credit carryforwards	268.4		236.4		95.9		81.7		112.9		95.5
Net operating losses carryforwards - federal	173.3		250.9		69.6		113.1		75.4		105.1
Regulatory liability - IPL’s tax benefit riders	34.7		66.1		34.7		66.1		—		—
Net operating losses carryforwards - state	32.9		38.3		0.6		1.1		0.1		3.6
Other	87.9		85.4		35.8		35.6		23.6		24.2
Total deferred tax assets	597.2		677.1		236.6		297.6		212.0		228.4
Total deferred tax liabilities, net		$2,570.2		$2,381.2		$1,511.8		$1,378.0		$971.6		$1,005.4

Summary Of Tax Credit Carryforwards

At December 31, 2016, carryforwards and expiration dates were estimated as follows (in millions):

	Range of Expiration Dates	Alliant Energy		IPL		WPL
Federal net operating losses	2030-2034		$506		$206		$215
State net operating losses	2018-2034	673		12		2
Federal tax credits	2022-2036	274		100		113

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)	2013	-	2015
Consolidated Iowa income tax returns (b)	2013	-	2015
Wisconsin combined tax returns (c)	2012	-	2015

(a) The federal tax returns for 2013 and 2014 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.