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Benefit Plans (Tables)
 9 Months Ended
Sep. 30, 2021
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 Energy20212020202120202021202020212020
Service cost$2$3$8$8$1$1$3$3
Interest cost91026321235
Expected return on plan assets(17)(17)(51)(52)(1)(1)(3)(4)
Amortization of prior service credit(1)—(1)—————
Amortization of actuarial loss10929261—32
Settlement losses (a)———4————
$3$5$11$18$2$2$6$6
Defined Benefit Pension PlansOPEB Plans
Three MonthsNine MonthsThree MonthsNine Months
IPL20212020202120202021202020212020
Service cost$1$2$5$5$—$—$1$1
Interest cost4512151122
Expected return on plan assets(8)(8)(24)(24)(1)(1)(3)(3)
Amortization of actuarial loss541311——11
$2$3$6$7$—$—$1$1
Defined Benefit Pension PlansOPEB Plans
Three MonthsNine MonthsThree MonthsNine Months
WPL20212020202120202021202020212020
Service cost$1$1$3$3$1$—$1$1
Interest cost351114—112
Expected return on plan assets(8)(8)(23)(23)—(1)—(1)
Amortization of actuarial loss5414121122
$1$2$5$6$2$1$4$4

(a)Settlement losses related to payments made to retired executives of Alliant Energy.
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 MonthsThree MonthsNine MonthsThree MonthsNine Months
202120202021202020212020202120202021202020212020
Compensation expense$4$5$9$10$2$3$5$6$2$2$4$4
Income tax benefits1133—112——11
Schedule Of Equity-based Compensation Plans Activity
For the nine months ended September 30, 2021, performance shares, performance restricted stock units and restricted stock units were granted to key employees 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 shares73,112$46.19
Performance restricted stock units73,11248.66
Restricted stock units80,15248.65
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 Energy20212020202120202021202020212020
Service cost$2$3$8$8$1$1$3$3
Interest cost91026321235
Expected return on plan assets(17)(17)(51)(52)(1)(1)(3)(4)
Amortization of prior service credit(1)—(1)—————
Amortization of actuarial loss10929261—32
Settlement losses (a)———4————
$3$5$11$18$2$2$6$6
Defined Benefit Pension PlansOPEB Plans
Three MonthsNine MonthsThree MonthsNine Months
IPL20212020202120202021202020212020
Service cost$1$2$5$5$—$—$1$1
Interest cost4512151122
Expected return on plan assets(8)(8)(24)(24)(1)(1)(3)(3)
Amortization of actuarial loss541311——11
$2$3$6$7$—$—$1$1
Defined Benefit Pension PlansOPEB Plans
Three MonthsNine MonthsThree MonthsNine Months
WPL20212020202120202021202020212020
Service cost$1$1$3$3$1$—$1$1
Interest cost351114—112
Expected return on plan assets(8)(8)(23)(23)—(1)—(1)
Amortization of actuarial loss5414121122
$1$2$5$6$2$1$4$4

(a)Settlement losses related to payments made to retired executives of Alliant Energy.
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 MonthsThree MonthsNine MonthsThree MonthsNine Months
202120202021202020212020202120202021202020212020
Compensation expense$4$5$9$10$2$3$5$6$2$2$4$4
Income tax benefits1133—112——11
Schedule Of Equity-based Compensation Plans Activity
For the nine months ended September 30, 2021, performance shares, performance restricted stock units and restricted stock units were granted to key employees 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 shares73,112$46.19
Performance restricted stock units73,11248.66
Restricted stock units80,15248.65
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 Energy20212020202120202021202020212020
Service cost$2$3$8$8$1$1$3$3
Interest cost91026321235
Expected return on plan assets(17)(17)(51)(52)(1)(1)(3)(4)
Amortization of prior service credit(1)—(1)—————
Amortization of actuarial loss10929261—32
Settlement losses (a)———4————
$3$5$11$18$2$2$6$6
Defined Benefit Pension PlansOPEB Plans
Three MonthsNine MonthsThree MonthsNine Months
IPL20212020202120202021202020212020
Service cost$1$2$5$5$—$—$1$1
Interest cost4512151122
Expected return on plan assets(8)(8)(24)(24)(1)(1)(3)(3)
Amortization of actuarial loss541311——11
$2$3$6$7$—$—$1$1
Defined Benefit Pension PlansOPEB Plans
Three MonthsNine MonthsThree MonthsNine Months
WPL20212020202120202021202020212020
Service cost$1$1$3$3$1$—$1$1
Interest cost351114—112
Expected return on plan assets(8)(8)(23)(23)—(1)—(1)
Amortization of actuarial loss5414121122
$1$2$5$6$2$1$4$4

(a)Settlement losses related to payments made to retired executives of Alliant Energy.
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 MonthsThree MonthsNine MonthsThree MonthsNine Months
202120202021202020212020202120202021202020212020
Compensation expense$4$5$9$10$2$3$5$6$2$2$4$4
Income tax benefits1133—112——11
Schedule Of Equity-based Compensation Plans Activity
For the nine months ended September 30, 2021, performance shares, performance restricted stock units and restricted stock units were granted to key employees 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 shares73,112$46.19
Performance restricted stock units73,11248.66
Restricted stock units80,15248.65