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Benefit Plans (Tables)
 9 Months Ended
Sep. 30, 2023
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 Energy20232022202320222023202220232022
Service cost$2$3$4$7$1$—$2$2
Interest cost12935273174
Expected return on plan assets(14)(18)(40)(52)(2)—(4)(3)
Amortization of prior service credit(1)—(1)—————
Amortization of actuarial loss782124—112
$6$2$19$6$2$2$6$5
Defined Benefit Pension PlansOPEB Plans
Three MonthsNine MonthsThree MonthsNine Months
IPL20232022202320222023202220232022
Service cost$—$1$2$4$—$—$—$1
Interest cost6416121132
Expected return on plan assets(6)(7)(19)(23)(1)(1)(3)(3)
Amortization of actuarial loss23810——1—
$2$1$7$3$—$—$1$—
Defined Benefit Pension PlansOPEB Plans
Three MonthsNine MonthsThree MonthsNine Months
WPL20232022202320222023202220232022
Service cost$—$—$1$2$1$—$1$—
Interest cost5415121132
Expected return on plan assets(5)(7)(16)(23)(1)—(1)—
Amortization of actuarial loss341012———1
$3$1$10$3$1$1$3$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
202320222023202220232022202320222023202220232022
Compensation expense$4$3$10$9$2$2$5$5$2$1$4$4
Income tax benefits11331—11——11
Schedule Of Equity-based Compensation Plans Activity
For the nine months ended September 30, 2023, performance shares, performance restricted stock units and restricted stock units were granted to key employees under existing 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 shares108,513$55.68
Performance restricted stock units123,99052.71
Restricted stock units105,98252.77
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 Energy20232022202320222023202220232022
Service cost$2$3$4$7$1$—$2$2
Interest cost12935273174
Expected return on plan assets(14)(18)(40)(52)(2)—(4)(3)
Amortization of prior service credit(1)—(1)—————
Amortization of actuarial loss782124—112
$6$2$19$6$2$2$6$5
Defined Benefit Pension PlansOPEB Plans
Three MonthsNine MonthsThree MonthsNine Months
IPL20232022202320222023202220232022
Service cost$—$1$2$4$—$—$—$1
Interest cost6416121132
Expected return on plan assets(6)(7)(19)(23)(1)(1)(3)(3)
Amortization of actuarial loss23810——1—
$2$1$7$3$—$—$1$—
Defined Benefit Pension PlansOPEB Plans
Three MonthsNine MonthsThree MonthsNine Months
WPL20232022202320222023202220232022
Service cost$—$—$1$2$1$—$1$—
Interest cost5415121132
Expected return on plan assets(5)(7)(16)(23)(1)—(1)—
Amortization of actuarial loss341012———1
$3$1$10$3$1$1$3$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
202320222023202220232022202320222023202220232022
Compensation expense$4$3$10$9$2$2$5$5$2$1$4$4
Income tax benefits11331—11——11
Schedule Of Equity-based Compensation Plans Activity
For the nine months ended September 30, 2023, performance shares, performance restricted stock units and restricted stock units were granted to key employees under existing 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 shares108,513$55.68
Performance restricted stock units123,99052.71
Restricted stock units105,98252.77
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 Energy20232022202320222023202220232022
Service cost$2$3$4$7$1$—$2$2
Interest cost12935273174
Expected return on plan assets(14)(18)(40)(52)(2)—(4)(3)
Amortization of prior service credit(1)—(1)—————
Amortization of actuarial loss782124—112
$6$2$19$6$2$2$6$5
Defined Benefit Pension PlansOPEB Plans
Three MonthsNine MonthsThree MonthsNine Months
IPL20232022202320222023202220232022
Service cost$—$1$2$4$—$—$—$1
Interest cost6416121132
Expected return on plan assets(6)(7)(19)(23)(1)(1)(3)(3)
Amortization of actuarial loss23810——1—
$2$1$7$3$—$—$1$—
Defined Benefit Pension PlansOPEB Plans
Three MonthsNine MonthsThree MonthsNine Months
WPL20232022202320222023202220232022
Service cost$—$—$1$2$1$—$1$—
Interest cost5415121132
Expected return on plan assets(5)(7)(16)(23)(1)—(1)—
Amortization of actuarial loss341012———1
$3$1$10$3$1$1$3$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
202320222023202220232022202320222023202220232022
Compensation expense$4$3$10$9$2$2$5$5$2$1$4$4
Income tax benefits11331—11——11
Schedule Of Equity-based Compensation Plans Activity
For the nine months ended September 30, 2023, performance shares, performance restricted stock units and restricted stock units were granted to key employees under existing 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 shares108,513$55.68
Performance restricted stock units123,99052.71
Restricted stock units105,98252.77