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Benefit Plans (Tables)
 9 Months Ended
Sep. 30, 2024
Defined Benefit Plan Disclosure [Line Items]  
Net Periodic Benefit Costs 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 are for their plan participants covered under plans they sponsor, as well as amounts directly assigned to them related to certain participants in the Alliant Energy and Corporate Services sponsored plans.
Defined Benefit Pension PlansOPEB Plans
Three MonthsNine MonthsThree MonthsNine Months
Alliant Energy20242023202420232024202320242023
Service cost$1$2$3$4$1$1$2$2
Interest cost121234352367
Expected return on plan assets(14)(14)(41)(40)(2)(2)(4)(4)
Amortization of prior service credit—(1)—(1)————
Amortization of actuarial loss671821———1
$5$6$14$19$1$2$4$6
Defined Benefit Pension PlansOPEB Plans
Three MonthsNine MonthsThree MonthsNine Months
IPL20242023202420232024202320242023
Service cost$1$—$2$2$—$—$—$—
Interest cost5615161133
Expected return on plan assets(7)(6)(20)(19)(1)(1)(3)(3)
Amortization of actuarial loss2278———1
$1$2$4$7$—$—$—$1
Defined Benefit Pension PlansOPEB Plans
Three MonthsNine MonthsThree MonthsNine Months
WPL20242023202420232024202320242023
Service cost$—$—$1$1$—$1$—$1
Interest cost5515151133
Expected return on plan assets(6)(5)(18)(16)(1)(1)(1)(1)
Amortization of actuarial loss33910————
$2$3$7$10$—$1$2$3
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 EnergyIPLWPL
Three MonthsNine Months Three MonthsNine Months Three MonthsNine Months
202420232024202320242023202420232024202320242023
Compensation expense$3$4$10$10$2$2$5$5$1$2$4$4
Income tax benefits1133—111——11
Schedule Of Equity-based Compensation Plans Activity
For the nine months ended September 30, 2024, performance shares and restricted stock units were granted to key employees under the equity-based compensation plans as follows. These shares and units will be paid out in shares of common stock, and are therefore accounted for as equity awards.
Weighted Average
GrantsGrant Date Fair Value
Performance shares (total shareowner return metric)127,267$46.04
Performance shares (net income and diversity metrics) (formerly granted as performance restricted stock units)145,44948.49
Restricted stock units128,62048.57
IPL [Member]  
Defined Benefit Plan Disclosure [Line Items]  
Net Periodic Benefit Costs 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 are for their plan participants covered under plans they sponsor, as well as amounts directly assigned to them related to certain participants in the Alliant Energy and Corporate Services sponsored plans.
Defined Benefit Pension PlansOPEB Plans
Three MonthsNine MonthsThree MonthsNine Months
Alliant Energy20242023202420232024202320242023
Service cost$1$2$3$4$1$1$2$2
Interest cost121234352367
Expected return on plan assets(14)(14)(41)(40)(2)(2)(4)(4)
Amortization of prior service credit—(1)—(1)————
Amortization of actuarial loss671821———1
$5$6$14$19$1$2$4$6
Defined Benefit Pension PlansOPEB Plans
Three MonthsNine MonthsThree MonthsNine Months
IPL20242023202420232024202320242023
Service cost$1$—$2$2$—$—$—$—
Interest cost5615161133
Expected return on plan assets(7)(6)(20)(19)(1)(1)(3)(3)
Amortization of actuarial loss2278———1
$1$2$4$7$—$—$—$1
Defined Benefit Pension PlansOPEB Plans
Three MonthsNine MonthsThree MonthsNine Months
WPL20242023202420232024202320242023
Service cost$—$—$1$1$—$1$—$1
Interest cost5515151133
Expected return on plan assets(6)(5)(18)(16)(1)(1)(1)(1)
Amortization of actuarial loss33910————
$2$3$7$10$—$1$2$3
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 EnergyIPLWPL
Three MonthsNine Months Three MonthsNine Months Three MonthsNine Months
202420232024202320242023202420232024202320242023
Compensation expense$3$4$10$10$2$2$5$5$1$2$4$4
Income tax benefits1133—111——11
Schedule Of Equity-based Compensation Plans Activity
For the nine months ended September 30, 2024, performance shares and restricted stock units were granted to key employees under the equity-based compensation plans as follows. These shares and units will be paid out in shares of common stock, and are therefore accounted for as equity awards.
Weighted Average
GrantsGrant Date Fair Value
Performance shares (total shareowner return metric)127,267$46.04
Performance shares (net income and diversity metrics) (formerly granted as performance restricted stock units)145,44948.49
Restricted stock units128,62048.57
WPL [Member]  
Defined Benefit Plan Disclosure [Line Items]  
Net Periodic Benefit Costs 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 are for their plan participants covered under plans they sponsor, as well as amounts directly assigned to them related to certain participants in the Alliant Energy and Corporate Services sponsored plans.
Defined Benefit Pension PlansOPEB Plans
Three MonthsNine MonthsThree MonthsNine Months
Alliant Energy20242023202420232024202320242023
Service cost$1$2$3$4$1$1$2$2
Interest cost121234352367
Expected return on plan assets(14)(14)(41)(40)(2)(2)(4)(4)
Amortization of prior service credit—(1)—(1)————
Amortization of actuarial loss671821———1
$5$6$14$19$1$2$4$6
Defined Benefit Pension PlansOPEB Plans
Three MonthsNine MonthsThree MonthsNine Months
IPL20242023202420232024202320242023
Service cost$1$—$2$2$—$—$—$—
Interest cost5615161133
Expected return on plan assets(7)(6)(20)(19)(1)(1)(3)(3)
Amortization of actuarial loss2278———1
$1$2$4$7$—$—$—$1
Defined Benefit Pension PlansOPEB Plans
Three MonthsNine MonthsThree MonthsNine Months
WPL20242023202420232024202320242023
Service cost$—$—$1$1$—$1$—$1
Interest cost5515151133
Expected return on plan assets(6)(5)(18)(16)(1)(1)(1)(1)
Amortization of actuarial loss33910————
$2$3$7$10$—$1$2$3
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 EnergyIPLWPL
Three MonthsNine Months Three MonthsNine Months Three MonthsNine Months
202420232024202320242023202420232024202320242023
Compensation expense$3$4$10$10$2$2$5$5$1$2$4$4
Income tax benefits1133—111——11
Schedule Of Equity-based Compensation Plans Activity
For the nine months ended September 30, 2024, performance shares and restricted stock units were granted to key employees under the equity-based compensation plans as follows. These shares and units will be paid out in shares of common stock, and are therefore accounted for as equity awards.
Weighted Average
GrantsGrant Date Fair Value
Performance shares (total shareowner return metric)127,267$46.04
Performance shares (net income and diversity metrics) (formerly granted as performance restricted stock units)145,44948.49
Restricted stock units128,62048.57