Income Taxes (Tables)

12 Months Ended

Dec. 31, 2018

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
	2018			2017			2016			2018			2017			2016			2018			2017			2016
Current tax expense (benefit):
Federal		($1.0	)		($41.0	)		$1.8			$14.9			($27.9	)		($12.8	)		($9.2	)		$5.5			($22.3	)
State	(5.1		)	8.5			17.2			(7.1		)	1.6			15.5			(4.4		)	2.5			1.1
IPL’s tax benefit riders	(13.2		)	(40.4		)	(44.2		)	(13.2		)	(40.4		)	(44.2		)	—			—			—
Deferred tax expense (benefit):
Federal	67.9			159.5			112.8			9.5			72.5			59.1			43.8			55.0			112.3
State	29.8			12.3			4.9			7.3			(2.2		)	(9.0		)	22.1			16.6			20.8
Production tax credits	(29.5		)	(31.1		)	(31.8		)	(14.0		)	(14.1		)	(14.0		)	(15.5		)	(17.0		)	(17.8		)
Investment tax credits	(1.2		)	(1.1		)	(1.3		)	(0.6		)	(0.4		)	(0.5		)	(0.6		)	(0.7		)	(0.8		)
		$47.7			$66.7			$59.4			($3.2	)		($10.9	)		($5.9	)		$36.2			$61.9			$93.3

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
	2018		2017		2016		2018		2017		2016		2018		2017		2016
Statutory federal income tax rate	21.0	%	35.0	%	35.0	%	21.0	%	35.0	%	35.0	%	21.0	%	35.0	%	35.0	%
State income taxes, net of federal benefits	7.0		5.5		5.4		7.7		6.5		6.4		6.2		5.1		5.1
Effect of rate-making on property-related differences	(7.6	)	(8.5	)	(8.5	)	(14.0	)	(19.1	)	(16.2	)	(2.3	)	(1.7	)	(0.7	)
Production tax credits	(5.2	)	(6.1	)	(7.2	)	(5.2	)	(6.7	)	(6.3	)	(6.4	)	(7.1	)	(6.2	)
IPL’s tax benefit riders	(2.3	)	(7.6	)	(10.0	)	(4.9	)	(18.7	)	(20.1	)	—		—		—
Adjustment for prior period taxes	(2.3	)	(1.5	)	(0.8	)	(4.8	)	(3.4	)	(1.2	)	(0.2	)	—		(0.1	)
Federal Tax Reform adjustments	(1.0	)	(3.4	)	—		(0.4	)	1.7		—		(2.3	)	(5.8	)	—
Other items, net	(1.2	)	(0.9	)	(0.5	)	(0.6	)	(0.3	)	(0.3	)	(1.2	)	(0.6	)	(0.5	)
Overall income tax rate	8.4	%	12.5	%	13.4	%	(1.2	%)	(5.0	%)	(2.7	%)	14.8	%	24.9	%	32.6	%

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
	2018			2017			2018			2017			2018			2017
Deferred tax liabilities:
Property		$1,975.5			$1,852.7			$1,158.4			$1,102.6			$735.2			$674.2
ATC Holdings	102.4			86.4			—			—			—			—
Other	80.5			75.9			69.4			63.4			34.4			36.5
Total deferred tax liabilities	2,158.4			2,015.0			1,227.8			1,166.0			769.6			710.7
Deferred tax assets:
Federal credit carryforwards	299.1			260.7			133.2			113.1			147.4			131.0
Net operating losses carryforwards - federal	158.6			174.4			114.1			107.4			26.4			43.7
Net operating losses carryforwards - state	47.0			41.3			0.9			0.9			0.5			0.2
Other	59.8			69.2			22.8			34.5			14.1			14.7
Subtotal deferred tax assets	564.5			545.6			271.0			255.9			188.4			189.6
Valuation allowances	(9.2		)	(9.0		)	(0.5		)	(0.6		)	(0.8		)	(1.3		)
Total deferred tax assets	555.3			536.6			270.5			255.3			187.6			188.3
Total deferred tax liabilities, net		$1,603.1			$1,478.4			$957.3			$910.7			$582.0			$522.4

Summary Of Tax Credit Carryforwards

At December 31, 2018, carryforwards and expiration dates were estimated as follows (in millions):

	Range of Expiration Dates	Alliant Energy		IPL		WPL
Federal net operating losses	2031-2037		$766		$551		$126
State net operating losses	2018-2038	792		13		8
Federal tax credits	2022-2038	299		133		147

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)	2015	-	2017
Consolidated Iowa income tax returns (b)	2015	-	2017
Wisconsin combined tax returns (c)	2014	-	2017

(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 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
	2018			2017			2016			2018			2017			2016			2018			2017			2016
Current tax expense (benefit):
Federal		($1.0	)		($41.0	)		$1.8			$14.9			($27.9	)		($12.8	)		($9.2	)		$5.5			($22.3	)
State	(5.1		)	8.5			17.2			(7.1		)	1.6			15.5			(4.4		)	2.5			1.1
IPL’s tax benefit riders	(13.2		)	(40.4		)	(44.2		)	(13.2		)	(40.4		)	(44.2		)	—			—			—
Deferred tax expense (benefit):
Federal	67.9			159.5			112.8			9.5			72.5			59.1			43.8			55.0			112.3
State	29.8			12.3			4.9			7.3			(2.2		)	(9.0		)	22.1			16.6			20.8
Production tax credits	(29.5		)	(31.1		)	(31.8		)	(14.0		)	(14.1		)	(14.0		)	(15.5		)	(17.0		)	(17.8		)
Investment tax credits	(1.2		)	(1.1		)	(1.3		)	(0.6		)	(0.4		)	(0.5		)	(0.6		)	(0.7		)	(0.8		)
		$47.7			$66.7			$59.4			($3.2	)		($10.9	)		($5.9	)		$36.2			$61.9			$93.3

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
	2018		2017		2016		2018		2017		2016		2018		2017		2016
Statutory federal income tax rate	21.0	%	35.0	%	35.0	%	21.0	%	35.0	%	35.0	%	21.0	%	35.0	%	35.0	%
State income taxes, net of federal benefits	7.0		5.5		5.4		7.7		6.5		6.4		6.2		5.1		5.1
Effect of rate-making on property-related differences	(7.6	)	(8.5	)	(8.5	)	(14.0	)	(19.1	)	(16.2	)	(2.3	)	(1.7	)	(0.7	)
Production tax credits	(5.2	)	(6.1	)	(7.2	)	(5.2	)	(6.7	)	(6.3	)	(6.4	)	(7.1	)	(6.2	)
IPL’s tax benefit riders	(2.3	)	(7.6	)	(10.0	)	(4.9	)	(18.7	)	(20.1	)	—		—		—
Adjustment for prior period taxes	(2.3	)	(1.5	)	(0.8	)	(4.8	)	(3.4	)	(1.2	)	(0.2	)	—		(0.1	)
Federal Tax Reform adjustments	(1.0	)	(3.4	)	—		(0.4	)	1.7		—		(2.3	)	(5.8	)	—
Other items, net	(1.2	)	(0.9	)	(0.5	)	(0.6	)	(0.3	)	(0.3	)	(1.2	)	(0.6	)	(0.5	)
Overall income tax rate	8.4	%	12.5	%	13.4	%	(1.2	%)	(5.0	%)	(2.7	%)	14.8	%	24.9	%	32.6	%

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
	2018			2017			2018			2017			2018			2017
Deferred tax liabilities:
Property		$1,975.5			$1,852.7			$1,158.4			$1,102.6			$735.2			$674.2
ATC Holdings	102.4			86.4			—			—			—			—
Other	80.5			75.9			69.4			63.4			34.4			36.5
Total deferred tax liabilities	2,158.4			2,015.0			1,227.8			1,166.0			769.6			710.7
Deferred tax assets:
Federal credit carryforwards	299.1			260.7			133.2			113.1			147.4			131.0
Net operating losses carryforwards - federal	158.6			174.4			114.1			107.4			26.4			43.7
Net operating losses carryforwards - state	47.0			41.3			0.9			0.9			0.5			0.2
Other	59.8			69.2			22.8			34.5			14.1			14.7
Subtotal deferred tax assets	564.5			545.6			271.0			255.9			188.4			189.6
Valuation allowances	(9.2		)	(9.0		)	(0.5		)	(0.6		)	(0.8		)	(1.3		)
Total deferred tax assets	555.3			536.6			270.5			255.3			187.6			188.3
Total deferred tax liabilities, net		$1,603.1			$1,478.4			$957.3			$910.7			$582.0			$522.4

Summary Of Tax Credit Carryforwards

At December 31, 2018, carryforwards and expiration dates were estimated as follows (in millions):

	Range of Expiration Dates	Alliant Energy		IPL		WPL
Federal net operating losses	2031-2037		$766		$551		$126
State net operating losses	2018-2038	792		13		8
Federal tax credits	2022-2038	299		133		147

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)	2015	-	2017
Consolidated Iowa income tax returns (b)	2015	-	2017
Wisconsin combined tax returns (c)	2014	-	2017

(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 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
	2018			2017			2016			2018			2017			2016			2018			2017			2016
Current tax expense (benefit):
Federal		($1.0	)		($41.0	)		$1.8			$14.9			($27.9	)		($12.8	)		($9.2	)		$5.5			($22.3	)
State	(5.1		)	8.5			17.2			(7.1		)	1.6			15.5			(4.4		)	2.5			1.1
IPL’s tax benefit riders	(13.2		)	(40.4		)	(44.2		)	(13.2		)	(40.4		)	(44.2		)	—			—			—
Deferred tax expense (benefit):
Federal	67.9			159.5			112.8			9.5			72.5			59.1			43.8			55.0			112.3
State	29.8			12.3			4.9			7.3			(2.2		)	(9.0		)	22.1			16.6			20.8
Production tax credits	(29.5		)	(31.1		)	(31.8		)	(14.0		)	(14.1		)	(14.0		)	(15.5		)	(17.0		)	(17.8		)
Investment tax credits	(1.2		)	(1.1		)	(1.3		)	(0.6		)	(0.4		)	(0.5		)	(0.6		)	(0.7		)	(0.8		)
		$47.7			$66.7			$59.4			($3.2	)		($10.9	)		($5.9	)		$36.2			$61.9			$93.3

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
	2018		2017		2016		2018		2017		2016		2018		2017		2016
Statutory federal income tax rate	21.0	%	35.0	%	35.0	%	21.0	%	35.0	%	35.0	%	21.0	%	35.0	%	35.0	%
State income taxes, net of federal benefits	7.0		5.5		5.4		7.7		6.5		6.4		6.2		5.1		5.1
Effect of rate-making on property-related differences	(7.6	)	(8.5	)	(8.5	)	(14.0	)	(19.1	)	(16.2	)	(2.3	)	(1.7	)	(0.7	)
Production tax credits	(5.2	)	(6.1	)	(7.2	)	(5.2	)	(6.7	)	(6.3	)	(6.4	)	(7.1	)	(6.2	)
IPL’s tax benefit riders	(2.3	)	(7.6	)	(10.0	)	(4.9	)	(18.7	)	(20.1	)	—		—		—
Adjustment for prior period taxes	(2.3	)	(1.5	)	(0.8	)	(4.8	)	(3.4	)	(1.2	)	(0.2	)	—		(0.1	)
Federal Tax Reform adjustments	(1.0	)	(3.4	)	—		(0.4	)	1.7		—		(2.3	)	(5.8	)	—
Other items, net	(1.2	)	(0.9	)	(0.5	)	(0.6	)	(0.3	)	(0.3	)	(1.2	)	(0.6	)	(0.5	)
Overall income tax rate	8.4	%	12.5	%	13.4	%	(1.2	%)	(5.0	%)	(2.7	%)	14.8	%	24.9	%	32.6	%

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
	2018			2017			2018			2017			2018			2017
Deferred tax liabilities:
Property		$1,975.5			$1,852.7			$1,158.4			$1,102.6			$735.2			$674.2
ATC Holdings	102.4			86.4			—			—			—			—
Other	80.5			75.9			69.4			63.4			34.4			36.5
Total deferred tax liabilities	2,158.4			2,015.0			1,227.8			1,166.0			769.6			710.7
Deferred tax assets:
Federal credit carryforwards	299.1			260.7			133.2			113.1			147.4			131.0
Net operating losses carryforwards - federal	158.6			174.4			114.1			107.4			26.4			43.7
Net operating losses carryforwards - state	47.0			41.3			0.9			0.9			0.5			0.2
Other	59.8			69.2			22.8			34.5			14.1			14.7
Subtotal deferred tax assets	564.5			545.6			271.0			255.9			188.4			189.6
Valuation allowances	(9.2		)	(9.0		)	(0.5		)	(0.6		)	(0.8		)	(1.3		)
Total deferred tax assets	555.3			536.6			270.5			255.3			187.6			188.3
Total deferred tax liabilities, net		$1,603.1			$1,478.4			$957.3			$910.7			$582.0			$522.4

Summary Of Tax Credit Carryforwards

At December 31, 2018, carryforwards and expiration dates were estimated as follows (in millions):

	Range of Expiration Dates	Alliant Energy		IPL		WPL
Federal net operating losses	2031-2037		$766		$551		$126
State net operating losses	2018-2038	792		13		8
Federal tax credits	2022-2038	299		133		147

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)	2015	-	2017
Consolidated Iowa income tax returns (b)	2015	-	2017
Wisconsin combined tax returns (c)	2014	-	2017

(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.