XML 23 R31.htm IDEA: XBRL DOCUMENT
v3.19.3

Benefit Plans (Tables) | 9 Months Ended
--- | ---
Sep. 30, 2019
Defined Benefit Plan Disclosure [Line Items] |
Defined Benefit Pension And Other Postretirement Benefits Plans | The components of net periodic benefit costs for sponsored defined benefit pension and OPEB plans for the three and nine months ended September 30 are included below (in millions). For IPL and WPL, amounts represent their current and former employees covered under plans they sponsor, as well as amounts directly assigned to them related to their current and former employees who are participants in the Alliant Energy and Corporate Services sponsored plans.
| Defined Benefit Pension Plans |  | OPEB Plans
| Three Months |  | Nine Months |  | Three Months |  | Nine Months
Alliant Energy | 2019 |  | 2018 |  | 2019 |  | 2018 |  | 2019 |  | 2018 |  | 2019 |  | 2018
Service cost |  | $2.5 |  |  |  | $3.1 |  |  |  | $7.3 |  |  |  | $9.1 |  |  |  | $0.8 |  |  |  | $1.0 |  |  |  | $2.5 |  |  |  | $3.1 |
Interest cost | 12.5 |  |  | 11.7 |  |  | 37.4 |  |  | 35.1 |  |  | 2.2 |  |  | 2.0 |  |  | 6.4 |  |  | 5.8 |
Expected return on plan assets | (15.1 | ) |  | (17.4 | ) |  | (45.1 | ) |  | (52.3 | ) |  | (1.2 | ) |  | (1.5 | ) |  | (3.7 | ) |  | (4.5 | )
Amortization of prior service credit | (0.2 | ) |  | (0.2 | ) |  | (0.5 | ) |  | (0.5 | ) |  | (0.1 | ) |  | — |  |  | (0.2 | ) |  | (0.1 | )
Amortization of actuarial loss | 9.1 |  |  | 8.8 |  |  | 27.3 |  |  | 26.4 |  |  | 0.8 |  |  | 0.8 |  |  | 2.4 |  |  | 2.5 |
|  | $8.8 |  |  |  | $6.0 |  |  |  | $26.4 |  |  |  | $17.8 |  |  |  | $2.5 |  |  |  | $2.3 |  |  |  | $7.4 |  |  |  | $6.8 |
| Defined Benefit Pension Plans |  | OPEB Plans
| Three Months |  | Nine Months |  | Three Months |  | Nine Months
IPL | 2019 |  | 2018 |  | 2019 |  | 2018 |  | 2019 |  | 2018 |  | 2019 |  | 2018
Service cost |  | $1.6 |  |  |  | $1.8 |  |  |  | $4.6 |  |  |  | $5.5 |  |  |  | $0.3 |  |  |  | $0.4 |  |  |  | $1.0 |  |  |  | $1.3 |
Interest cost | 5.6 |  |  | 5.3 |  |  | 17.0 |  |  | 16.0 |  |  | 0.8 |  |  | 0.7 |  |  | 2.5 |  |  | 2.3 |
Expected return on plan assets | (7.0 | ) |  | (8.1 | ) |  | (21.1 | ) |  | (24.4 | ) |  | (0.9 | ) |  | (1.1 | ) |  | (2.7 | ) |  | (3.3 | )
Amortization of prior service credit | (0.1 | ) |  | — |  |  | (0.2 | ) |  | (0.1 | ) |  | — |  |  | — |  |  | — |  |  | — |
Amortization of actuarial loss | 3.9 |  |  | 3.7 |  |  | 11.8 |  |  | 11.2 |  |  | 0.4 |  |  | 0.4 |  |  | 1.1 |  |  | 1.0 |
|  | $4.0 |  |  |  | $2.7 |  |  |  | $12.1 |  |  |  | $8.2 |  |  |  | $0.6 |  |  |  | $0.4 |  |  |  | $1.9 |  |  |  | $1.3 |
| Defined Benefit Pension Plans |  | OPEB Plans
| Three Months |  | Nine Months |  | Three Months |  | Nine Months
WPL | 2019 |  | 2018 |  | 2019 |  | 2018 |  | 2019 |  | 2018 |  | 2019 |  | 2018
Service cost |  | $0.9 |  |  |  | $1.1 |  |  |  | $2.6 |  |  |  | $3.3 |  |  |  | $0.3 |  |  |  | $0.4 |  |  |  | $0.9 |  |  |  | $1.2 |
Interest cost | 5.3 |  |  | 5.0 |  |  | 16.1 |  |  | 15.1 |  |  | 0.9 |  |  | 0.8 |  |  | 2.6 |  |  | 2.3 |
Expected return on plan assets | (6.5 | ) |  | (7.6 | ) |  | (19.6 | ) |  | (22.8 | ) |  | (0.2 | ) |  | (0.2 | ) |  | (0.5 | ) |  | (0.5 | )
Amortization of prior service credit | — |  |  | — |  |  | (0.1 | ) |  | (0.1 | ) |  | — |  |  | — |  |  | (0.1 | ) |  | (0.1 | )
Amortization of actuarial loss | 4.4 |  |  | 4.3 |  |  | 13.2 |  |  | 12.9 |  |  | 0.4 |  |  | 0.5 |  |  | 1.2 |  |  | 1.5 |
|  | $4.1 |  |  |  | $2.8 |  |  |  | $12.2 |  |  |  | $8.4 |  |  |  | $1.4 |  |  |  | $1.5 |  |  |  | $4.1 |  |  |  | $4.4 |
Recognized Compensation Expense And Income Tax Benefits | A summary of compensation expense, including amounts allocated to IPL and WPL, and the related income tax benefits recognized for share-based compensation awards for the three and nine months ended September 30 was as follows (in millions):
| Alliant Energy |  | IPL |  | WPL
| Three Months |  | Nine Months |  | Three Months |  | Nine Months |  | Three Months |  | Nine Months
| 2019 |  | 2018 |  | 2019 |  | 2018 |  | 2019 |  | 2018 |  | 2019 |  | 2018 |  | 2019 |  | 2018 |  | 2019 |  | 2018
Compensation expense |  | $7.5 |  |  |  | $4.2 |  |  |  | $15.6 |  |  |  | $12.6 |  |  |  | $4.2 |  |  |  | $2.4 |  |  |  | $8.7 |  |  |  | $7.0 |  |  |  | $3.0 |  |  |  | $1.7 |  |  |  | $6.2 |  |  |  | $5.1 |
Income tax benefits | 2.1 |  |  | 1.2 |  |  | 4.4 |  |  | 3.6 |  |  | 1.2 |  |  | 0.7 |  |  | 2.5 |  |  | 2.1 |  |  | 0.8 |  |  | 0.5 |  |  | 1.7 |  |  | 1.4 |
IPL [Member] |
Defined Benefit Plan Disclosure [Line Items] |
Defined Benefit Pension And Other Postretirement Benefits Plans | The components of net periodic benefit costs for sponsored defined benefit pension and OPEB plans for the three and nine months ended September 30 are included below (in millions). For IPL and WPL, amounts represent their current and former employees covered under plans they sponsor, as well as amounts directly assigned to them related to their current and former employees who are participants in the Alliant Energy and Corporate Services sponsored plans.
| Defined Benefit Pension Plans |  | OPEB Plans
| Three Months |  | Nine Months |  | Three Months |  | Nine Months
Alliant Energy | 2019 |  | 2018 |  | 2019 |  | 2018 |  | 2019 |  | 2018 |  | 2019 |  | 2018
Service cost |  | $2.5 |  |  |  | $3.1 |  |  |  | $7.3 |  |  |  | $9.1 |  |  |  | $0.8 |  |  |  | $1.0 |  |  |  | $2.5 |  |  |  | $3.1 |
Interest cost | 12.5 |  |  | 11.7 |  |  | 37.4 |  |  | 35.1 |  |  | 2.2 |  |  | 2.0 |  |  | 6.4 |  |  | 5.8 |
Expected return on plan assets | (15.1 | ) |  | (17.4 | ) |  | (45.1 | ) |  | (52.3 | ) |  | (1.2 | ) |  | (1.5 | ) |  | (3.7 | ) |  | (4.5 | )
Amortization of prior service credit | (0.2 | ) |  | (0.2 | ) |  | (0.5 | ) |  | (0.5 | ) |  | (0.1 | ) |  | — |  |  | (0.2 | ) |  | (0.1 | )
Amortization of actuarial loss | 9.1 |  |  | 8.8 |  |  | 27.3 |  |  | 26.4 |  |  | 0.8 |  |  | 0.8 |  |  | 2.4 |  |  | 2.5 |
|  | $8.8 |  |  |  | $6.0 |  |  |  | $26.4 |  |  |  | $17.8 |  |  |  | $2.5 |  |  |  | $2.3 |  |  |  | $7.4 |  |  |  | $6.8 |
| Defined Benefit Pension Plans |  | OPEB Plans
| Three Months |  | Nine Months |  | Three Months |  | Nine Months
IPL | 2019 |  | 2018 |  | 2019 |  | 2018 |  | 2019 |  | 2018 |  | 2019 |  | 2018
Service cost |  | $1.6 |  |  |  | $1.8 |  |  |  | $4.6 |  |  |  | $5.5 |  |  |  | $0.3 |  |  |  | $0.4 |  |  |  | $1.0 |  |  |  | $1.3 |
Interest cost | 5.6 |  |  | 5.3 |  |  | 17.0 |  |  | 16.0 |  |  | 0.8 |  |  | 0.7 |  |  | 2.5 |  |  | 2.3 |
Expected return on plan assets | (7.0 | ) |  | (8.1 | ) |  | (21.1 | ) |  | (24.4 | ) |  | (0.9 | ) |  | (1.1 | ) |  | (2.7 | ) |  | (3.3 | )
Amortization of prior service credit | (0.1 | ) |  | — |  |  | (0.2 | ) |  | (0.1 | ) |  | — |  |  | — |  |  | — |  |  | — |
Amortization of actuarial loss | 3.9 |  |  | 3.7 |  |  | 11.8 |  |  | 11.2 |  |  | 0.4 |  |  | 0.4 |  |  | 1.1 |  |  | 1.0 |
|  | $4.0 |  |  |  | $2.7 |  |  |  | $12.1 |  |  |  | $8.2 |  |  |  | $0.6 |  |  |  | $0.4 |  |  |  | $1.9 |  |  |  | $1.3 |
| Defined Benefit Pension Plans |  | OPEB Plans
| Three Months |  | Nine Months |  | Three Months |  | Nine Months
WPL | 2019 |  | 2018 |  | 2019 |  | 2018 |  | 2019 |  | 2018 |  | 2019 |  | 2018
Service cost |  | $0.9 |  |  |  | $1.1 |  |  |  | $2.6 |  |  |  | $3.3 |  |  |  | $0.3 |  |  |  | $0.4 |  |  |  | $0.9 |  |  |  | $1.2 |
Interest cost | 5.3 |  |  | 5.0 |  |  | 16.1 |  |  | 15.1 |  |  | 0.9 |  |  | 0.8 |  |  | 2.6 |  |  | 2.3 |
Expected return on plan assets | (6.5 | ) |  | (7.6 | ) |  | (19.6 | ) |  | (22.8 | ) |  | (0.2 | ) |  | (0.2 | ) |  | (0.5 | ) |  | (0.5 | )
Amortization of prior service credit | — |  |  | — |  |  | (0.1 | ) |  | (0.1 | ) |  | — |  |  | — |  |  | (0.1 | ) |  | (0.1 | )
Amortization of actuarial loss | 4.4 |  |  | 4.3 |  |  | 13.2 |  |  | 12.9 |  |  | 0.4 |  |  | 0.5 |  |  | 1.2 |  |  | 1.5 |
|  | $4.1 |  |  |  | $2.8 |  |  |  | $12.2 |  |  |  | $8.4 |  |  |  | $1.4 |  |  |  | $1.5 |  |  |  | $4.1 |  |  |  | $4.4 |
Recognized Compensation Expense And Income Tax Benefits | A summary of compensation expense, including amounts allocated to IPL and WPL, and the related income tax benefits recognized for share-based compensation awards for the three and nine months ended September 30 was as follows (in millions):
| Alliant Energy |  | IPL |  | WPL
| Three Months |  | Nine Months |  | Three Months |  | Nine Months |  | Three Months |  | Nine Months
| 2019 |  | 2018 |  | 2019 |  | 2018 |  | 2019 |  | 2018 |  | 2019 |  | 2018 |  | 2019 |  | 2018 |  | 2019 |  | 2018
Compensation expense |  | $7.5 |  |  |  | $4.2 |  |  |  | $15.6 |  |  |  | $12.6 |  |  |  | $4.2 |  |  |  | $2.4 |  |  |  | $8.7 |  |  |  | $7.0 |  |  |  | $3.0 |  |  |  | $1.7 |  |  |  | $6.2 |  |  |  | $5.1 |
Income tax benefits | 2.1 |  |  | 1.2 |  |  | 4.4 |  |  | 3.6 |  |  | 1.2 |  |  | 0.7 |  |  | 2.5 |  |  | 2.1 |  |  | 0.8 |  |  | 0.5 |  |  | 1.7 |  |  | 1.4 |
WPL [Member] |
Defined Benefit Plan Disclosure [Line Items] |
Defined Benefit Pension And Other Postretirement Benefits Plans | The components of net periodic benefit costs for sponsored defined benefit pension and OPEB plans for the three and nine months ended September 30 are included below (in millions). For IPL and WPL, amounts represent their current and former employees covered under plans they sponsor, as well as amounts directly assigned to them related to their current and former employees who are participants in the Alliant Energy and Corporate Services sponsored plans.
| Defined Benefit Pension Plans |  | OPEB Plans
| Three Months |  | Nine Months |  | Three Months |  | Nine Months
Alliant Energy | 2019 |  | 2018 |  | 2019 |  | 2018 |  | 2019 |  | 2018 |  | 2019 |  | 2018
Service cost |  | $2.5 |  |  |  | $3.1 |  |  |  | $7.3 |  |  |  | $9.1 |  |  |  | $0.8 |  |  |  | $1.0 |  |  |  | $2.5 |  |  |  | $3.1 |
Interest cost | 12.5 |  |  | 11.7 |  |  | 37.4 |  |  | 35.1 |  |  | 2.2 |  |  | 2.0 |  |  | 6.4 |  |  | 5.8 |
Expected return on plan assets | (15.1 | ) |  | (17.4 | ) |  | (45.1 | ) |  | (52.3 | ) |  | (1.2 | ) |  | (1.5 | ) |  | (3.7 | ) |  | (4.5 | )
Amortization of prior service credit | (0.2 | ) |  | (0.2 | ) |  | (0.5 | ) |  | (0.5 | ) |  | (0.1 | ) |  | — |  |  | (0.2 | ) |  | (0.1 | )
Amortization of actuarial loss | 9.1 |  |  | 8.8 |  |  | 27.3 |  |  | 26.4 |  |  | 0.8 |  |  | 0.8 |  |  | 2.4 |  |  | 2.5 |
|  | $8.8 |  |  |  | $6.0 |  |  |  | $26.4 |  |  |  | $17.8 |  |  |  | $2.5 |  |  |  | $2.3 |  |  |  | $7.4 |  |  |  | $6.8 |
| Defined Benefit Pension Plans |  | OPEB Plans
| Three Months |  | Nine Months |  | Three Months |  | Nine Months
IPL | 2019 |  | 2018 |  | 2019 |  | 2018 |  | 2019 |  | 2018 |  | 2019 |  | 2018
Service cost |  | $1.6 |  |  |  | $1.8 |  |  |  | $4.6 |  |  |  | $5.5 |  |  |  | $0.3 |  |  |  | $0.4 |  |  |  | $1.0 |  |  |  | $1.3 |
Interest cost | 5.6 |  |  | 5.3 |  |  | 17.0 |  |  | 16.0 |  |  | 0.8 |  |  | 0.7 |  |  | 2.5 |  |  | 2.3 |
Expected return on plan assets | (7.0 | ) |  | (8.1 | ) |  | (21.1 | ) |  | (24.4 | ) |  | (0.9 | ) |  | (1.1 | ) |  | (2.7 | ) |  | (3.3 | )
Amortization of prior service credit | (0.1 | ) |  | — |  |  | (0.2 | ) |  | (0.1 | ) |  | — |  |  | — |  |  | — |  |  | — |
Amortization of actuarial loss | 3.9 |  |  | 3.7 |  |  | 11.8 |  |  | 11.2 |  |  | 0.4 |  |  | 0.4 |  |  | 1.1 |  |  | 1.0 |
|  | $4.0 |  |  |  | $2.7 |  |  |  | $12.1 |  |  |  | $8.2 |  |  |  | $0.6 |  |  |  | $0.4 |  |  |  | $1.9 |  |  |  | $1.3 |
| Defined Benefit Pension Plans |  | OPEB Plans
| Three Months |  | Nine Months |  | Three Months |  | Nine Months
WPL | 2019 |  | 2018 |  | 2019 |  | 2018 |  | 2019 |  | 2018 |  | 2019 |  | 2018
Service cost |  | $0.9 |  |  |  | $1.1 |  |  |  | $2.6 |  |  |  | $3.3 |  |  |  | $0.3 |  |  |  | $0.4 |  |  |  | $0.9 |  |  |  | $1.2 |
Interest cost | 5.3 |  |  | 5.0 |  |  | 16.1 |  |  | 15.1 |  |  | 0.9 |  |  | 0.8 |  |  | 2.6 |  |  | 2.3 |
Expected return on plan assets | (6.5 | ) |  | (7.6 | ) |  | (19.6 | ) |  | (22.8 | ) |  | (0.2 | ) |  | (0.2 | ) |  | (0.5 | ) |  | (0.5 | )
Amortization of prior service credit | — |  |  | — |  |  | (0.1 | ) |  | (0.1 | ) |  | — |  |  | — |  |  | (0.1 | ) |  | (0.1 | )
Amortization of actuarial loss | 4.4 |  |  | 4.3 |  |  | 13.2 |  |  | 12.9 |  |  | 0.4 |  |  | 0.5 |  |  | 1.2 |  |  | 1.5 |
|  | $4.1 |  |  |  | $2.8 |  |  |  | $12.2 |  |  |  | $8.4 |  |  |  | $1.4 |  |  |  | $1.5 |  |  |  | $4.1 |  |  |  | $4.4 |
Recognized Compensation Expense And Income Tax Benefits | A summary of compensation expense, including amounts allocated to IPL and WPL, and the related income tax benefits recognized for share-based compensation awards for the three and nine months ended September 30 was as follows (in millions):
| Alliant Energy |  | IPL |  | WPL
| Three Months |  | Nine Months |  | Three Months |  | Nine Months |  | Three Months |  | Nine Months
| 2019 |  | 2018 |  | 2019 |  | 2018 |  | 2019 |  | 2018 |  | 2019 |  | 2018 |  | 2019 |  | 2018 |  | 2019 |  | 2018
Compensation expense |  | $7.5 |  |  |  | $4.2 |  |  |  | $15.6 |  |  |  | $12.6 |  |  |  | $4.2 |  |  |  | $2.4 |  |  |  | $8.7 |  |  |  | $7.0 |  |  |  | $3.0 |  |  |  | $1.7 |  |  |  | $6.2 |  |  |  | $5.1 |
Income tax benefits | 2.1 |  |  | 1.2 |  |  | 4.4 |  |  | 3.6 |  |  | 1.2 |  |  | 0.7 |  |  | 2.5 |  |  | 2.1 |  |  | 0.8 |  |  | 0.5 |  |  | 1.7 |  |  | 1.4 |

X
- Definition Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table. + References No definition available. + Details
Name: | us-gaap_DefinedBenefitPlanDisclosureLineItems
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

X
- Definition Tabular disclosure of allocation of amount expensed and capitalized for award under share-based payment arrangement to statement of income or comprehensive income and statement of financial position. Includes, but is not limited to, corresponding line item in financial statement. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (h)(1) -URI http://asc.fasb.org/extlink&oid=116856206&loc=d3e5070-113901 Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SAB Topic 14.F) -URI http://asc.fasb.org/extlink&oid=115993241&loc=d3e301413-122809 Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 1 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=116856206&loc=d3e5047-113901 + Details
Name: | us-gaap_ScheduleOfEmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsTextBlock
Namespace Prefix: | us-gaap_
Data Type: | nonnum:textBlockItemType
Balance Type: | na
Period Type: | duration

X
- Definition Tabular disclosure of the components of net benefit costs for pension plans and/or other employee benefit plans including service cost, interest cost, expected return on plan assets, gain (loss), prior service cost or credit, transition asset or obligation, and gain (loss) recognized due to settlements or curtailments. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (h) -URI http://asc.fasb.org/extlink&oid=118255775&loc=d3e1928-114920 + Details
Name: | us-gaap_ScheduleOfNetBenefitCostsTableTextBlock
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: |