Income Taxes (Tables)

12 Months Ended

Dec. 31, 2020

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
	2020	2019	2018	2020	2019	2018	2020	2019	2018
Current tax expense (benefit):
Federal	$1	($7)	($1)	$6	($11)	$15	($11)	$12	($9)
State	8	24	(5)	(1)	24	(7)	7	13	(5)
IPL’s tax benefit riders	—	(4)	(13)	—	(4)	(13)	—	—	—
Deferred tax expense (benefit):
Federal	22	70	68	30	26	10	(9)	31	44
State	8	42	30	(2)	31	7	10	6	22
Production tax credits	(95)	(55)	(30)	(80)	(42)	(14)	(15)	(13)	(15)
Investment tax credits	(1)	(1)	(1)	—	—	(1)	(1)	—	(1)
	($57)	$69	$48	($47)	$24	($3)	($19)	$49	$36

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
	2020		2019		2018		2020		2019		2018		2020		2019		2018
Statutory federal income tax rate	21	%	21	%	21	%	21	%	21	%	21	%	21	%	21	%	21	%
State income taxes, net of federal benefits	2		7		7		(1)		8		8		6		6		6
Production tax credits	(17)		(9)		(5)		(28)		(13)		(5)		(7)		(5)		(7)
Amortization of excess deferred taxes (Refer to Note 2)	(13)		(1)		(1)		(5)		—		—		(26)		(2)		—
Effect of rate-making on property-related differences	(3)		(6)		(8)		(4)		(10)		(14)		(2)		(3)		(2)
Adjustment for prior period taxes	1		1		(2)		1		3		(5)		—		—		—
IPL’s tax benefit riders	—		(1)		(2)		—		(1)		(5)		—		—		—
Federal Tax Reform adjustments	—		—		(1)		—		—		—		—		—		(2)
Other items, net	(1)		(1)		(1)		—		—		(1)		—		—		(1)
Overall income tax rate	(10	%)	11	%	8	%	(16	%)	8	%	(1	%)	(8	%)	17	%	15	%

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
	2020	2019	2020	2019	2020	2019
Deferred tax liabilities:
Property	$2,232	$2,022	$1,312	$1,184	$854	$770
ATC Holdings	116	111	—	—	—	—
Other	101	84	83	76	41	32
Total deferred tax liabilities	2,449	2,217	1,395	1,260	895	802
Deferred tax assets:
Federal credit carryforwards	454	355	258	175	175	160
Net operating losses carryforwards - federal	77	60	71	56	1	1
Net operating losses carryforwards - state	37	37	1	1	—	—
Other	73	61	30	20	18	16
Subtotal deferred tax assets	641	513	360	252	194	177
Valuation allowances	(6)	(10)	—	—	(1)	(1)
Total deferred tax assets	635	503	360	252	193	176
Total deferred tax liabilities, net	$1,814	$1,714	$1,035	$1,008	$702	$626

Summary Of Tax Credit Carryforwards

At December 31, 2020, carryforwards and expiration dates were estimated as follows (in millions):

	Range of Expiration Dates	Alliant Energy	IPL	WPL
Federal net operating losses	2037	$366	$339	$3
State net operating losses	2021-2040	622	10	2
Federal tax credits	2022-2040	454	258	175

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)	2017	-	2019
Consolidated Iowa income tax returns (b)	2017	-	2019
Wisconsin combined tax returns (c)	2016	-	2019

(a)The 2017 federal tax return is 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
	2020	2019	2018	2020	2019	2018	2020	2019	2018
Current tax expense (benefit):
Federal	$1	($7)	($1)	$6	($11)	$15	($11)	$12	($9)
State	8	24	(5)	(1)	24	(7)	7	13	(5)
IPL’s tax benefit riders	—	(4)	(13)	—	(4)	(13)	—	—	—
Deferred tax expense (benefit):
Federal	22	70	68	30	26	10	(9)	31	44
State	8	42	30	(2)	31	7	10	6	22
Production tax credits	(95)	(55)	(30)	(80)	(42)	(14)	(15)	(13)	(15)
Investment tax credits	(1)	(1)	(1)	—	—	(1)	(1)	—	(1)
	($57)	$69	$48	($47)	$24	($3)	($19)	$49	$36

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
	2020		2019		2018		2020		2019		2018		2020		2019		2018
Statutory federal income tax rate	21	%	21	%	21	%	21	%	21	%	21	%	21	%	21	%	21	%
State income taxes, net of federal benefits	2		7		7		(1)		8		8		6		6		6
Production tax credits	(17)		(9)		(5)		(28)		(13)		(5)		(7)		(5)		(7)
Amortization of excess deferred taxes (Refer to Note 2)	(13)		(1)		(1)		(5)		—		—		(26)		(2)		—
Effect of rate-making on property-related differences	(3)		(6)		(8)		(4)		(10)		(14)		(2)		(3)		(2)
Adjustment for prior period taxes	1		1		(2)		1		3		(5)		—		—		—
IPL’s tax benefit riders	—		(1)		(2)		—		(1)		(5)		—		—		—
Federal Tax Reform adjustments	—		—		(1)		—		—		—		—		—		(2)
Other items, net	(1)		(1)		(1)		—		—		(1)		—		—		(1)
Overall income tax rate	(10	%)	11	%	8	%	(16	%)	8	%	(1	%)	(8	%)	17	%	15	%

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
	2020	2019	2020	2019	2020	2019
Deferred tax liabilities:
Property	$2,232	$2,022	$1,312	$1,184	$854	$770
ATC Holdings	116	111	—	—	—	—
Other	101	84	83	76	41	32
Total deferred tax liabilities	2,449	2,217	1,395	1,260	895	802
Deferred tax assets:
Federal credit carryforwards	454	355	258	175	175	160
Net operating losses carryforwards - federal	77	60	71	56	1	1
Net operating losses carryforwards - state	37	37	1	1	—	—
Other	73	61	30	20	18	16
Subtotal deferred tax assets	641	513	360	252	194	177
Valuation allowances	(6)	(10)	—	—	(1)	(1)
Total deferred tax assets	635	503	360	252	193	176
Total deferred tax liabilities, net	$1,814	$1,714	$1,035	$1,008	$702	$626

Summary Of Tax Credit Carryforwards

At December 31, 2020, carryforwards and expiration dates were estimated as follows (in millions):

	Range of Expiration Dates	Alliant Energy	IPL	WPL
Federal net operating losses	2037	$366	$339	$3
State net operating losses	2021-2040	622	10	2
Federal tax credits	2022-2040	454	258	175

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)	2017	-	2019
Consolidated Iowa income tax returns (b)	2017	-	2019
Wisconsin combined tax returns (c)	2016	-	2019

(a)The 2017 federal tax return is 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
	2020	2019	2018	2020	2019	2018	2020	2019	2018
Current tax expense (benefit):
Federal	$1	($7)	($1)	$6	($11)	$15	($11)	$12	($9)
State	8	24	(5)	(1)	24	(7)	7	13	(5)
IPL’s tax benefit riders	—	(4)	(13)	—	(4)	(13)	—	—	—
Deferred tax expense (benefit):
Federal	22	70	68	30	26	10	(9)	31	44
State	8	42	30	(2)	31	7	10	6	22
Production tax credits	(95)	(55)	(30)	(80)	(42)	(14)	(15)	(13)	(15)
Investment tax credits	(1)	(1)	(1)	—	—	(1)	(1)	—	(1)
	($57)	$69	$48	($47)	$24	($3)	($19)	$49	$36

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
	2020		2019		2018		2020		2019		2018		2020		2019		2018
Statutory federal income tax rate	21	%	21	%	21	%	21	%	21	%	21	%	21	%	21	%	21	%
State income taxes, net of federal benefits	2		7		7		(1)		8		8		6		6		6
Production tax credits	(17)		(9)		(5)		(28)		(13)		(5)		(7)		(5)		(7)
Amortization of excess deferred taxes (Refer to Note 2)	(13)		(1)		(1)		(5)		—		—		(26)		(2)		—
Effect of rate-making on property-related differences	(3)		(6)		(8)		(4)		(10)		(14)		(2)		(3)		(2)
Adjustment for prior period taxes	1		1		(2)		1		3		(5)		—		—		—
IPL’s tax benefit riders	—		(1)		(2)		—		(1)		(5)		—		—		—
Federal Tax Reform adjustments	—		—		(1)		—		—		—		—		—		(2)
Other items, net	(1)		(1)		(1)		—		—		(1)		—		—		(1)
Overall income tax rate	(10	%)	11	%	8	%	(16	%)	8	%	(1	%)	(8	%)	17	%	15	%

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
	2020	2019	2020	2019	2020	2019
Deferred tax liabilities:
Property	$2,232	$2,022	$1,312	$1,184	$854	$770
ATC Holdings	116	111	—	—	—	—
Other	101	84	83	76	41	32
Total deferred tax liabilities	2,449	2,217	1,395	1,260	895	802
Deferred tax assets:
Federal credit carryforwards	454	355	258	175	175	160
Net operating losses carryforwards - federal	77	60	71	56	1	1
Net operating losses carryforwards - state	37	37	1	1	—	—
Other	73	61	30	20	18	16
Subtotal deferred tax assets	641	513	360	252	194	177
Valuation allowances	(6)	(10)	—	—	(1)	(1)
Total deferred tax assets	635	503	360	252	193	176
Total deferred tax liabilities, net	$1,814	$1,714	$1,035	$1,008	$702	$626

Summary Of Tax Credit Carryforwards

At December 31, 2020, carryforwards and expiration dates were estimated as follows (in millions):

	Range of Expiration Dates	Alliant Energy	IPL	WPL
Federal net operating losses	2037	$366	$339	$3
State net operating losses	2021-2040	622	10	2
Federal tax credits	2022-2040	454	258	175

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)	2017	-	2019
Consolidated Iowa income tax returns (b)	2017	-	2019
Wisconsin combined tax returns (c)	2016	-	2019

(a)The 2017 federal tax return is 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.