XML 34 R14.htm IDEA: XBRL DOCUMENT
v3.19.1

Income Taxes | 3 Months Ended
--- | ---
Mar. 31, 2019
Income Taxes [Line Items] |
Income Taxes | INCOME TAXES Income Tax Rates - The overall income tax rates shown in the following table were computed by dividing income taxes by income before income taxes.
| Alliant Energy |  | IPL |  | WPL
Three Months Ended March 31 | 2019 |  | 2018 |  | 2019 |  | 2018 |  | 2019 |  | 2018
Statutory federal income tax rate | 21.0 | % |  | 21.0 | % |  | 21.0 | % |  | 21.0 | % |  | 21.0 | % |  | 21.0 | %
State income taxes, net of federal benefits | 6.7 |  |  | 7.5 |  |  | 7.2 |  |  | 8.5 |  |  | 6.2 |  |  | 6.2 |
Production tax credits | (9.2 | ) |  | (5.5 | ) |  | (14.0 | ) |  | (5.4 | ) |  | (4.9 | ) |  | (6.7 | )
Effect of rate-making on property-related differences | (5.6 | ) |  | (7.4 | ) |  | (9.2 | ) |  | (13.5 | ) |  | (2.3 | ) |  | (2.4 | )
Amortization of excess deferred taxes | (0.9 | ) |  | (0.4 | ) |  | (0.2 | ) |  | — |  |  | (1.4 | ) |  | (0.1 | )
IPL’s tax benefit riders | (0.7 | ) |  | (2.2 | ) |  | (1.5 | ) |  | (4.7 | ) |  | — |  |  | — |
Other items, net | (0.7 | ) |  | (1.0 | ) |  | 0.3 |  |  | — |  |  | (0.4 | ) |  | (0.2 | )
Overall income tax rate | 10.6 | % |  | 12.0 | % |  | 3.6 | % |  | 5.9 | % |  | 18.2 | % |  | 17.8 | %
Deferred Tax Assets and Liabilities - Carryforwards - At March 31, 2019, carryforwards and expiration dates were estimated as follows (in millions):
| Range of Expiration Dates |  | Alliant Energy |  | IPL |  | WPL
Federal net operating losses | 2031-2039 |  |  | $776 |  |  |  | $551 |  |  |  | $129 |
State net operating losses | 2019-2039 |  | 785 |  |  | 13 |  |  | 2 |
Federal tax credits | 2022-2039 |  | 307 |  |  | 138 |  |  | 151 |
IPL [Member] |
Income Taxes [Line Items] |
Income Taxes | INCOME TAXES Income Tax Rates - The overall income tax rates shown in the following table were computed by dividing income taxes by income before income taxes.
| Alliant Energy |  | IPL |  | WPL
Three Months Ended March 31 | 2019 |  | 2018 |  | 2019 |  | 2018 |  | 2019 |  | 2018
Statutory federal income tax rate | 21.0 | % |  | 21.0 | % |  | 21.0 | % |  | 21.0 | % |  | 21.0 | % |  | 21.0 | %
State income taxes, net of federal benefits | 6.7 |  |  | 7.5 |  |  | 7.2 |  |  | 8.5 |  |  | 6.2 |  |  | 6.2 |
Production tax credits | (9.2 | ) |  | (5.5 | ) |  | (14.0 | ) |  | (5.4 | ) |  | (4.9 | ) |  | (6.7 | )
Effect of rate-making on property-related differences | (5.6 | ) |  | (7.4 | ) |  | (9.2 | ) |  | (13.5 | ) |  | (2.3 | ) |  | (2.4 | )
Amortization of excess deferred taxes | (0.9 | ) |  | (0.4 | ) |  | (0.2 | ) |  | — |  |  | (1.4 | ) |  | (0.1 | )
IPL’s tax benefit riders | (0.7 | ) |  | (2.2 | ) |  | (1.5 | ) |  | (4.7 | ) |  | — |  |  | — |
Other items, net | (0.7 | ) |  | (1.0 | ) |  | 0.3 |  |  | — |  |  | (0.4 | ) |  | (0.2 | )
Overall income tax rate | 10.6 | % |  | 12.0 | % |  | 3.6 | % |  | 5.9 | % |  | 18.2 | % |  | 17.8 | %
Deferred Tax Assets and Liabilities - Carryforwards - At March 31, 2019, carryforwards and expiration dates were estimated as follows (in millions):
| Range of Expiration Dates |  | Alliant Energy |  | IPL |  | WPL
Federal net operating losses | 2031-2039 |  |  | $776 |  |  |  | $551 |  |  |  | $129 |
State net operating losses | 2019-2039 |  | 785 |  |  | 13 |  |  | 2 |
Federal tax credits | 2022-2039 |  | 307 |  |  | 138 |  |  | 151 |
WPL [Member] |
Income Taxes [Line Items] |
Income Taxes | INCOME TAXES Income Tax Rates - The overall income tax rates shown in the following table were computed by dividing income taxes by income before income taxes.
| Alliant Energy |  | IPL |  | WPL
Three Months Ended March 31 | 2019 |  | 2018 |  | 2019 |  | 2018 |  | 2019 |  | 2018
Statutory federal income tax rate | 21.0 | % |  | 21.0 | % |  | 21.0 | % |  | 21.0 | % |  | 21.0 | % |  | 21.0 | %
State income taxes, net of federal benefits | 6.7 |  |  | 7.5 |  |  | 7.2 |  |  | 8.5 |  |  | 6.2 |  |  | 6.2 |
Production tax credits | (9.2 | ) |  | (5.5 | ) |  | (14.0 | ) |  | (5.4 | ) |  | (4.9 | ) |  | (6.7 | )
Effect of rate-making on property-related differences | (5.6 | ) |  | (7.4 | ) |  | (9.2 | ) |  | (13.5 | ) |  | (2.3 | ) |  | (2.4 | )
Amortization of excess deferred taxes | (0.9 | ) |  | (0.4 | ) |  | (0.2 | ) |  | — |  |  | (1.4 | ) |  | (0.1 | )
IPL’s tax benefit riders | (0.7 | ) |  | (2.2 | ) |  | (1.5 | ) |  | (4.7 | ) |  | — |  |  | — |
Other items, net | (0.7 | ) |  | (1.0 | ) |  | 0.3 |  |  | — |  |  | (0.4 | ) |  | (0.2 | )
Overall income tax rate | 10.6 | % |  | 12.0 | % |  | 3.6 | % |  | 5.9 | % |  | 18.2 | % |  | 17.8 | %
Deferred Tax Assets and Liabilities - Carryforwards - At March 31, 2019, carryforwards and expiration dates were estimated as follows (in millions):
| Range of Expiration Dates |  | Alliant Energy |  | IPL |  | WPL
Federal net operating losses | 2031-2039 |  |  | $776 |  |  |  | $551 |  |  |  | $129 |
State net operating losses | 2019-2039 |  | 785 |  |  | 13 |  |  | 2 |
Federal tax credits | 2022-2039 |  | 307 |  |  | 138 |  |  | 151 |

X
- Definition Income tax + References No definition available. + Details
Name: | lnt_IncomeTaxLineItems
Namespace Prefix: | lnt_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

X
- Definition The entire disclosure for income taxes. Disclosures may include net deferred tax liability or asset recognized in an enterprise's statement of financial position, net change during the year in the total valuation allowance, approximate tax effect of each type of temporary difference and carryforward that gives rise to a significant portion of deferred tax liabilities and deferred tax assets, utilization of a tax carryback, and tax uncertainties information. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 740 -URI http://asc.fasb.org/topic&trid=2144680 + Details
Name: | us-gaap_IncomeTaxDisclosureTextBlock
Namespace Prefix: | us-gaap_
Data Type: | nonnum:textBlockItemType
Balance Type: | na
Period Type: | duration

X
- Details
Name: | dei_LegalEntityAxis=lnt_IplMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | dei_LegalEntityAxis=lnt_WplMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |