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Benefit Plans | 3 Months Ended
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Mar. 31, 2016
Benefit Plans | BENEFIT PLANS NOTE 9(a) Pension and Other Postretirement Benefits Plans - Net Periodic Benefit Costs (Credits) - The components of net periodic benefit costs (credits) for sponsored defined benefit pension and OPEB plans for the three months ended March 31 are included in the tables below (in millions). In IPL’s and WPL’s tables below, the defined benefit pension plans costs represent those respective costs for their bargaining unit employees covered under the qualified plans that they sponsor, as well as amounts directly assigned to them related to their current and former non-bargaining employees who are participants in the Alliant Energy and Corporate Services sponsored qualified and non-qualified defined benefit pension plans. In IPL’s and WPL’s tables below, the OPEB plans costs (credits) represent respective costs (credits) for their employees, as well as amounts directly assigned to them related to their current and former non-bargaining employees who are participants in the Corporate Services sponsored OPEB plan.
| Defined Benefit Pension Plans |  | OPEB Plans
Alliant Energy | 2016 |  | 2015 |  | 2016 |  | 2015
Service cost |  | $3.2 |  |  |  | $4.0 |  |  |  | $1.3 |  |  |  | $1.4 |
Interest cost | 13.3 |  |  | 13.4 |  |  | 2.3 |  |  | 2.2 |
Expected return on plan assets | (16.4 | ) |  | (18.7 | ) |  | (1.5 | ) |  | (2.1 | )
Amortization of prior service credit | (0.1 | ) |  | (0.1 | ) |  | (1.0 | ) |  | (2.8 | )
Amortization of actuarial loss | 9.3 |  |  | 8.8 |  |  | 1.2 |  |  | 1.2 |
Additional benefit costs | — |  |  | 0.2 |  |  | — |  |  | — |
|  | $9.3 |  |  |  | $7.6 |  |  |  | $2.3 |  |  |  | ($0.1 | )
| Defined Benefit Pension Plans |  | OPEB Plans
IPL | 2016 |  | 2015 |  | 2016 |  | 2015
Service cost |  | $1.9 |  |  |  | $2.2 |  |  |  | $0.6 |  |  |  | $0.6 |
Interest cost | 6.1 |  |  | 6.2 |  |  | 1.0 |  |  | 0.9 |
Expected return on plan assets | (7.7 | ) |  | (8.9 | ) |  | (1.0 | ) |  | (1.4 | )
Amortization of prior service credit | — |  |  | — |  |  | (0.7 | ) |  | (1.5 | )
Amortization of actuarial loss | 4.1 |  |  | 3.8 |  |  | 0.6 |  |  | 0.6 |
|  | $4.4 |  |  |  | $3.3 |  |  |  | $0.5 |  |  |  | ($0.8 | )
| Defined Benefit Pension Plans |  | OPEB Plans
WPL | 2016 |  | 2015 |  | 2016 |  | 2015
Service cost |  | $1.2 |  |  |  | $1.4 |  |  |  | $0.5 |  |  |  | $0.6 |
Interest cost | 5.6 |  |  | 5.6 |  |  | 0.9 |  |  | 0.9 |
Expected return on plan assets | (7.1 | ) |  | (8.1 | ) |  | (0.2 | ) |  | (0.4 | )
Amortization of prior service cost (credit) | 0.1 |  |  | 0.1 |  |  | (0.2 | ) |  | (0.9 | )
Amortization of actuarial loss | 4.4 |  |  | 4.2 |  |  | 0.5 |  |  | 0.6 |
Additional benefit costs | — |  |  | 0.2 |  |  | — |  |  | — |
|  | $4.2 |  |  |  | $3.4 |  |  |  | $1.5 |  |  |  | $0.8 |
401(k) Savings Plans - A significant number of employees participate in defined contribution retirement plans (401(k) savings plans). For the three months ended March 31, costs related to the 401(k) savings plans, which are partially based on the participants’ contributions and include allocated costs associated with Corporate Services employees for IPL and WPL, were as follows (in millions):
| Alliant Energy |  | IPL |  | WPL
| 2016 |  | 2015 |  | 2016 |  | 2015 |  | 2016 |  | 2015
401(k) costs |  | $6.2 |  |  |  | $6.7 |  |  |  | $3.1 |  |  |  | $3.4 |  |  |  | $2.8 |  |  |  | $2.9 |
NOTE 9(b) Equity-based Compensation Plans - 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 months ended March 31 was as follows (in millions):
| Alliant Energy |  | IPL |  | WPL
| 2016 |  | 2015 |  | 2016 |  | 2015 |  | 2016 |  | 2015
Compensation expense |  | $5.3 |  |  |  | $3.2 |  |  |  | $2.8 |  |  |  | $1.7 |  |  |  | $2.3 |  |  |  | $1.4 |
Income tax benefits | 2.2 |  |  | 1.3 |  |  | 1.1 |  |  | 0.7 |  |  | 0.9 |  |  | 0.6 |
As of March 31, 2016, total unrecognized compensation cost related to share-based compensation awards was $12.9 million, which is expected to be recognized over a weighted average period of between one and two years. Share-based compensation expense is recognized on a straight-line basis over the requisite service periods and is primarily recorded in “Other operation and maintenance” in the income statements. Performance Shares and Performance Units - A summary of the performance shares and performance units activity, with amounts representing the target number of awards, was as follows:
| Performance Shares |  | Performance Units
| 2016 |  | 2015 |  | 2016 |  | 2015
Nonvested awards, January 1 | 144,215 |  |  | 144,424 |  |  | 58,206 |  |  | 63,665 |
Granted | 33,776 |  |  | 45,403 |  |  | 11,959 |  |  | 17,837 |
Vested | (49,093 | ) |  | (45,612 | ) |  | (21,380 | ) |  | (22,845 | )
Forfeited | (615 | ) |  | — |  |  | (382 | ) |  | (93 | )
Nonvested awards, March 31 | 128,283 |  |  | 144,215 |  |  | 48,403 |  |  | 58,564 |
Granted Awards - For the performance units granted in 2016, each performance unit’s value is based on the closing market price of one share of Alliant Energy’s common stock at the end of the performance period. For the performance units granted prior to 2016, each performance unit’s value is based on the closing market price of one share of Alliant Energy’s common stock on the grant date of the award. Vested Awards - During the three months ended March 31, certain performance shares and performance units vested, resulting in payouts (a combination of cash and common stock for the performance shares and cash only for the performance units) as follows:
| Performance Shares |  | Performance Units
| 2016 |  | 2015 |  | 2016 |  | 2015
| 2013 Grant |  | 2012 Grant |  | 2013 Grant |  | 2012 Grant
Performance awards vested | 49,093 |  |  | 45,612 |  |  | 21,380 |  |  | 22,845 |
Percentage of target number of performance awards | 165.0 | % |  | 167.5 | % |  | 165.0 | % |  | 167.5 | %
Aggregate payout value (in millions) |  | $5.1 |  |  |  | $5.1 |  |  |  | $1.7 |  |  |  | $1.6 |
Payout - cash (in millions) |  | $2.9 |  |  |  | $3.2 |  |  |  | $1.7 |  |  |  | $1.6 |
Payout - common stock shares issued | 11,204 |  |  | 10,975 |  |  | N/A |  | N/A
Fair Value of Awards - Information related to fair values of nonvested performance shares and performance units at March 31, 2016, by year of grant, was as follows:
| Performance Shares |  | Performance Units
| 2016 Grant |  | 2015 Grant |  | 2014 Grant |  | 2016 Grant |  | 2015 Grant |  | 2014 Grant
Nonvested awards | 33,161 |  |  | 45,403 |  |  | 49,719 |  |  | 11,959 |  |  | 17,209 |  |  | 19,235 |
Alliant Energy common stock closing price on March 31, 2016 |  | $74.28 |  |  |  | $74.28 |  |  |  | $74.28 |  |  |  | $74.28 |  |  | N/A |  | N/A
Alliant Energy common stock closing price on grant date | N/A |  | N/A |  | N/A |  | N/A |  |  | $65.09 |  |  |  | $53.77 |
Estimated payout percentage based on performance criteria | 108 | % |  | 90 | % |  | 138 | % |  | 108 | % |  | 90 | % |  | 138 | %
Fair values of each nonvested award |  | $80.22 |  |  |  | $66.85 |  |  |  | $102.51 |  |  |  | $80.22 |  |  |  | $58.58 |  |  |  | $74.20 |
At March 31, 2016, fair values of nonvested performance shares and performance units were calculated based on Alliant Energy’s stock price and anticipated total shareowner returns of Alliant Energy and its investor-owned utility peer group over the performance period. The portion of the fair values based on anticipated total shareowner returns was estimated using a model that incorporates the probability of meeting performance targets based on historical returns relative to the peer group. Performance Contingent Restricted Stock - A summary of the performance contingent restricted stock activity was as follows:
| 2016 |  | 2015
| Shares |  | Weighted Average Grant Date Fair Value |  | Shares |  | Weighted Average Grant Date Fair Value
Nonvested shares, January 1 | 95,122 |  |  |  | $59.17 |  |  | 98,812 |  |  |  | $50.69 |
Granted | — |  |  | — |  |  | 45,403 |  |  | 65.09 |
Vested (a) | — |  |  | — |  |  | (49,093 | ) |  | 47.58 |
Nonvested shares, March 31 | 95,122 |  |  | 59.17 |  |  | 95,122 |  |  | 59.17 |
(a) | In 2015, 49,093 performance contingent restricted shares granted in 2013 vested because the specified performance criteria for such shares were met.
Performance Restricted Stock Units and Performance Restricted Units - Alliant Energy granted new types of share-based compensation awards to key employees in the first quarter of 2016 referred to as performance restricted stock units, performance restricted units and key employee performance restricted units. Payouts of these units are based on the achievement of certain performance targets (currently specified growth of consolidated income from continuing operations) during the three-year performance period. The actual number of units that will be paid out upon vesting is dependent upon actual performance and may range from zero to 200% of the target number of units. If performance targets are not met during the performance period, these units are forfeited. Subject to achievement of the performance criteria, payouts of nonvested units are prorated in the event of retirement, death or disability during the first year of the performance period based on time worked during the first year of the period, and are prorated upon involuntary termination without cause based on time worked during the entire period. Subject to achievement of the performance criteria, payouts of units to participants who terminate employment after the first year of the performance period due to retirement, death or disability are not prorated. Participants’ nonvested units are forfeited if the participant voluntarily leaves Alliant Energy or is terminated for cause during the performance period. Performance Restricted Stock Units - Performance restricted stock units must be paid out in shares and are accounted for as equity awards. Each performance restricted stock unit’s value is based on the closing market price of one share of Alliant Energy’s common stock on the grant date of the award. A summary of the performance restricted stock units activity, with amounts representing the target number of units, was as follows:
| 2016
| Units |  | Weighted Average Grant Date Fair Value
Granted | 33,776 |  |  |  | $67.85 |
Forfeited | (615 | ) |  | 67.80 |
Nonvested units, March 31 | 33,161 |  |  | 67.85 |
Performance Restricted Units - Performance restricted units must be paid out in cash and are accounted for as liability awards. Each performance restricted unit’s value is based on the closing market price of one share of Alliant Energy’s common stock at the end of the performance period. A summary of the performance restricted units activity, with amounts representing the target number of units, was as follows:
| 2016
Granted | 11,959 |
Nonvested units, March 31 | 11,959 |
Key Employee Performance Restricted Units - Key employee performance restricted units must be paid out in cash and are accounted for as liability awards. Each key employee performance restricted unit’s value is based on the closing market price of one share of Alliant Energy’s common stock on the grant date of the award. A summary of the key employee performance restricted units activity, with amounts representing the target number of units, was as follows:
| 2016
| Units |  | Weighted Average Grant Date Fair Value
Granted | 22,528 |  |  |  | $67.80 |
Nonvested units, March 31 | 22,528 |  |  | 67.80 |
Restricted Stock Units and Restricted Units - Alliant Energy granted new types of share-based compensation awards to key employees in the first quarter of 2016 referred to as restricted stock units and restricted units. Payouts of these units are based on the expiration of a three-year time-vesting period. Payouts of nonvested units are prorated in the event of retirement, death or disability during the first year of the time-vesting period based on time worked during the first year of the period, and are prorated upon involuntary termination without cause based on time worked during the entire period. Upon expiration of the time-vesting period, payouts of units to participants who terminate employment after the first year of the period due to retirement, death or disability are not prorated. Participants’ nonvested units are forfeited if the participant voluntarily leaves Alliant Energy or is terminated for cause during the time-vesting period. Each restricted stock unit’s and restricted unit’s value is based on the closing market price of one share of Alliant Energy’s common stock at the end of the time-vesting period. Restricted stock units can be paid out in shares of Alliant Energy common stock, cash or a combination of cash and stock. Restricted units must be paid out in cash. Alliant Energy assumes it will make future payouts of its restricted stock units and restricted units in cash; therefore, restricted stock units and restricted units are accounted for as liability awards. A summary of the restricted stock units and restricted units activity was as follows:
| 2016
| Restricted Stock Units |  | Restricted Units
Granted | 28,952 |  |  | 10,251 |
Forfeited | (527 | ) |  | — |
Nonvested units, March 31 | 28,425 |  |  | 10,251 |
Performance-Contingent Cash Awards - A summary of the performance-contingent cash awards activity was as follows:
| 2016 |  | 2015
Nonvested awards, January 1 | 81,876 |  |  | 78,930 |
Granted | — |  |  | 41,105 |
Vested (a) | — |  |  | (37,332 | )
Forfeited | (382 | ) |  | (469 | )
Nonvested awards, March 31 | 81,494 |  |  | 82,234 |
(a) | In 2015, 37,332 performance-contingent cash awards granted in 2013 vested, resulting in cash payouts valued at $2.4 million.
IPL [Member] |
Benefit Plans | BENEFIT PLANS NOTE 9(a) Pension and Other Postretirement Benefits Plans - Net Periodic Benefit Costs (Credits) - The components of net periodic benefit costs (credits) for sponsored defined benefit pension and OPEB plans for the three months ended March 31 are included in the tables below (in millions). In IPL’s and WPL’s tables below, the defined benefit pension plans costs represent those respective costs for their bargaining unit employees covered under the qualified plans that they sponsor, as well as amounts directly assigned to them related to their current and former non-bargaining employees who are participants in the Alliant Energy and Corporate Services sponsored qualified and non-qualified defined benefit pension plans. In IPL’s and WPL’s tables below, the OPEB plans costs (credits) represent respective costs (credits) for their employees, as well as amounts directly assigned to them related to their current and former non-bargaining employees who are participants in the Corporate Services sponsored OPEB plan.
| Defined Benefit Pension Plans |  | OPEB Plans
Alliant Energy | 2016 |  | 2015 |  | 2016 |  | 2015
Service cost |  | $3.2 |  |  |  | $4.0 |  |  |  | $1.3 |  |  |  | $1.4 |
Interest cost | 13.3 |  |  | 13.4 |  |  | 2.3 |  |  | 2.2 |
Expected return on plan assets | (16.4 | ) |  | (18.7 | ) |  | (1.5 | ) |  | (2.1 | )
Amortization of prior service credit | (0.1 | ) |  | (0.1 | ) |  | (1.0 | ) |  | (2.8 | )
Amortization of actuarial loss | 9.3 |  |  | 8.8 |  |  | 1.2 |  |  | 1.2 |
Additional benefit costs | — |  |  | 0.2 |  |  | — |  |  | — |
|  | $9.3 |  |  |  | $7.6 |  |  |  | $2.3 |  |  |  | ($0.1 | )
| Defined Benefit Pension Plans |  | OPEB Plans
IPL | 2016 |  | 2015 |  | 2016 |  | 2015
Service cost |  | $1.9 |  |  |  | $2.2 |  |  |  | $0.6 |  |  |  | $0.6 |
Interest cost | 6.1 |  |  | 6.2 |  |  | 1.0 |  |  | 0.9 |
Expected return on plan assets | (7.7 | ) |  | (8.9 | ) |  | (1.0 | ) |  | (1.4 | )
Amortization of prior service credit | — |  |  | — |  |  | (0.7 | ) |  | (1.5 | )
Amortization of actuarial loss | 4.1 |  |  | 3.8 |  |  | 0.6 |  |  | 0.6 |
|  | $4.4 |  |  |  | $3.3 |  |  |  | $0.5 |  |  |  | ($0.8 | )
| Defined Benefit Pension Plans |  | OPEB Plans
WPL | 2016 |  | 2015 |  | 2016 |  | 2015
Service cost |  | $1.2 |  |  |  | $1.4 |  |  |  | $0.5 |  |  |  | $0.6 |
Interest cost | 5.6 |  |  | 5.6 |  |  | 0.9 |  |  | 0.9 |
Expected return on plan assets | (7.1 | ) |  | (8.1 | ) |  | (0.2 | ) |  | (0.4 | )
Amortization of prior service cost (credit) | 0.1 |  |  | 0.1 |  |  | (0.2 | ) |  | (0.9 | )
Amortization of actuarial loss | 4.4 |  |  | 4.2 |  |  | 0.5 |  |  | 0.6 |
Additional benefit costs | — |  |  | 0.2 |  |  | — |  |  | — |
|  | $4.2 |  |  |  | $3.4 |  |  |  | $1.5 |  |  |  | $0.8 |
401(k) Savings Plans - A significant number of employees participate in defined contribution retirement plans (401(k) savings plans). For the three months ended March 31, costs related to the 401(k) savings plans, which are partially based on the participants’ contributions and include allocated costs associated with Corporate Services employees for IPL and WPL, were as follows (in millions):
| Alliant Energy |  | IPL |  | WPL
| 2016 |  | 2015 |  | 2016 |  | 2015 |  | 2016 |  | 2015
401(k) costs |  | $6.2 |  |  |  | $6.7 |  |  |  | $3.1 |  |  |  | $3.4 |  |  |  | $2.8 |  |  |  | $2.9 |
NOTE 9(b) Equity-based Compensation Plans - 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 months ended March 31 was as follows (in millions):
| Alliant Energy |  | IPL |  | WPL
| 2016 |  | 2015 |  | 2016 |  | 2015 |  | 2016 |  | 2015
Compensation expense |  | $5.3 |  |  |  | $3.2 |  |  |  | $2.8 |  |  |  | $1.7 |  |  |  | $2.3 |  |  |  | $1.4 |
Income tax benefits | 2.2 |  |  | 1.3 |  |  | 1.1 |  |  | 0.7 |  |  | 0.9 |  |  | 0.6 |
As of March 31, 2016, total unrecognized compensation cost related to share-based compensation awards was $12.9 million, which is expected to be recognized over a weighted average period of between one and two years. Share-based compensation expense is recognized on a straight-line basis over the requisite service periods and is primarily recorded in “Other operation and maintenance” in the income statements. Performance Shares and Performance Units - A summary of the performance shares and performance units activity, with amounts representing the target number of awards, was as follows:
| Performance Shares |  | Performance Units
| 2016 |  | 2015 |  | 2016 |  | 2015
Nonvested awards, January 1 | 144,215 |  |  | 144,424 |  |  | 58,206 |  |  | 63,665 |
Granted | 33,776 |  |  | 45,403 |  |  | 11,959 |  |  | 17,837 |
Vested | (49,093 | ) |  | (45,612 | ) |  | (21,380 | ) |  | (22,845 | )
Forfeited | (615 | ) |  | — |  |  | (382 | ) |  | (93 | )
Nonvested awards, March 31 | 128,283 |  |  | 144,215 |  |  | 48,403 |  |  | 58,564 |
Granted Awards - For the performance units granted in 2016, each performance unit’s value is based on the closing market price of one share of Alliant Energy’s common stock at the end of the performance period. For the performance units granted prior to 2016, each performance unit’s value is based on the closing market price of one share of Alliant Energy’s common stock on the grant date of the award. Vested Awards - During the three months ended March 31, certain performance shares and performance units vested, resulting in payouts (a combination of cash and common stock for the performance shares and cash only for the performance units) as follows:
| Performance Shares |  | Performance Units
| 2016 |  | 2015 |  | 2016 |  | 2015
| 2013 Grant |  | 2012 Grant |  | 2013 Grant |  | 2012 Grant
Performance awards vested | 49,093 |  |  | 45,612 |  |  | 21,380 |  |  | 22,845 |
Percentage of target number of performance awards | 165.0 | % |  | 167.5 | % |  | 165.0 | % |  | 167.5 | %
Aggregate payout value (in millions) |  | $5.1 |  |  |  | $5.1 |  |  |  | $1.7 |  |  |  | $1.6 |
Payout - cash (in millions) |  | $2.9 |  |  |  | $3.2 |  |  |  | $1.7 |  |  |  | $1.6 |
Payout - common stock shares issued | 11,204 |  |  | 10,975 |  |  | N/A |  | N/A
Fair Value of Awards - Information related to fair values of nonvested performance shares and performance units at March 31, 2016, by year of grant, was as follows:
| Performance Shares |  | Performance Units
| 2016 Grant |  | 2015 Grant |  | 2014 Grant |  | 2016 Grant |  | 2015 Grant |  | 2014 Grant
Nonvested awards | 33,161 |  |  | 45,403 |  |  | 49,719 |  |  | 11,959 |  |  | 17,209 |  |  | 19,235 |
Alliant Energy common stock closing price on March 31, 2016 |  | $74.28 |  |  |  | $74.28 |  |  |  | $74.28 |  |  |  | $74.28 |  |  | N/A |  | N/A
Alliant Energy common stock closing price on grant date | N/A |  | N/A |  | N/A |  | N/A |  |  | $65.09 |  |  |  | $53.77 |
Estimated payout percentage based on performance criteria | 108 | % |  | 90 | % |  | 138 | % |  | 108 | % |  | 90 | % |  | 138 | %
Fair values of each nonvested award |  | $80.22 |  |  |  | $66.85 |  |  |  | $102.51 |  |  |  | $80.22 |  |  |  | $58.58 |  |  |  | $74.20 |
At March 31, 2016, fair values of nonvested performance shares and performance units were calculated based on Alliant Energy’s stock price and anticipated total shareowner returns of Alliant Energy and its investor-owned utility peer group over the performance period. The portion of the fair values based on anticipated total shareowner returns was estimated using a model that incorporates the probability of meeting performance targets based on historical returns relative to the peer group. Performance Contingent Restricted Stock - A summary of the performance contingent restricted stock activity was as follows:
| 2016 |  | 2015
| Shares |  | Weighted Average Grant Date Fair Value |  | Shares |  | Weighted Average Grant Date Fair Value
Nonvested shares, January 1 | 95,122 |  |  |  | $59.17 |  |  | 98,812 |  |  |  | $50.69 |
Granted | — |  |  | — |  |  | 45,403 |  |  | 65.09 |
Vested (a) | — |  |  | — |  |  | (49,093 | ) |  | 47.58 |
Nonvested shares, March 31 | 95,122 |  |  | 59.17 |  |  | 95,122 |  |  | 59.17 |
(a) | In 2015, 49,093 performance contingent restricted shares granted in 2013 vested because the specified performance criteria for such shares were met.
Performance Restricted Stock Units and Performance Restricted Units - Alliant Energy granted new types of share-based compensation awards to key employees in the first quarter of 2016 referred to as performance restricted stock units, performance restricted units and key employee performance restricted units. Payouts of these units are based on the achievement of certain performance targets (currently specified growth of consolidated income from continuing operations) during the three-year performance period. The actual number of units that will be paid out upon vesting is dependent upon actual performance and may range from zero to 200% of the target number of units. If performance targets are not met during the performance period, these units are forfeited. Subject to achievement of the performance criteria, payouts of nonvested units are prorated in the event of retirement, death or disability during the first year of the performance period based on time worked during the first year of the period, and are prorated upon involuntary termination without cause based on time worked during the entire period. Subject to achievement of the performance criteria, payouts of units to participants who terminate employment after the first year of the performance period due to retirement, death or disability are not prorated. Participants’ nonvested units are forfeited if the participant voluntarily leaves Alliant Energy or is terminated for cause during the performance period. Performance Restricted Stock Units - Performance restricted stock units must be paid out in shares and are accounted for as equity awards. Each performance restricted stock unit’s value is based on the closing market price of one share of Alliant Energy’s common stock on the grant date of the award. A summary of the performance restricted stock units activity, with amounts representing the target number of units, was as follows:
| 2016
| Units |  | Weighted Average Grant Date Fair Value
Granted | 33,776 |  |  |  | $67.85 |
Forfeited | (615 | ) |  | 67.80 |
Nonvested units, March 31 | 33,161 |  |  | 67.85 |
Performance Restricted Units - Performance restricted units must be paid out in cash and are accounted for as liability awards. Each performance restricted unit’s value is based on the closing market price of one share of Alliant Energy’s common stock at the end of the performance period. A summary of the performance restricted units activity, with amounts representing the target number of units, was as follows:
| 2016
Granted | 11,959 |
Nonvested units, March 31 | 11,959 |
Key Employee Performance Restricted Units - Key employee performance restricted units must be paid out in cash and are accounted for as liability awards. Each key employee performance restricted unit’s value is based on the closing market price of one share of Alliant Energy’s common stock on the grant date of the award. A summary of the key employee performance restricted units activity, with amounts representing the target number of units, was as follows:
| 2016
| Units |  | Weighted Average Grant Date Fair Value
Granted | 22,528 |  |  |  | $67.80 |
Nonvested units, March 31 | 22,528 |  |  | 67.80 |
Restricted Stock Units and Restricted Units - Alliant Energy granted new types of share-based compensation awards to key employees in the first quarter of 2016 referred to as restricted stock units and restricted units. Payouts of these units are based on the expiration of a three-year time-vesting period. Payouts of nonvested units are prorated in the event of retirement, death or disability during the first year of the time-vesting period based on time worked during the first year of the period, and are prorated upon involuntary termination without cause based on time worked during the entire period. Upon expiration of the time-vesting period, payouts of units to participants who terminate employment after the first year of the period due to retirement, death or disability are not prorated. Participants’ nonvested units are forfeited if the participant voluntarily leaves Alliant Energy or is terminated for cause during the time-vesting period. Each restricted stock unit’s and restricted unit’s value is based on the closing market price of one share of Alliant Energy’s common stock at the end of the time-vesting period. Restricted stock units can be paid out in shares of Alliant Energy common stock, cash or a combination of cash and stock. Restricted units must be paid out in cash. Alliant Energy assumes it will make future payouts of its restricted stock units and restricted units in cash; therefore, restricted stock units and restricted units are accounted for as liability awards. A summary of the restricted stock units and restricted units activity was as follows:
| 2016
| Restricted Stock Units |  | Restricted Units
Granted | 28,952 |  |  | 10,251 |
Forfeited | (527 | ) |  | — |
Nonvested units, March 31 | 28,425 |  |  | 10,251 |
Performance-Contingent Cash Awards - A summary of the performance-contingent cash awards activity was as follows:
| 2016 |  | 2015
Nonvested awards, January 1 | 81,876 |  |  | 78,930 |
Granted | — |  |  | 41,105 |
Vested (a) | — |  |  | (37,332 | )
Forfeited | (382 | ) |  | (469 | )
Nonvested awards, March 31 | 81,494 |  |  | 82,234 |
(a) | In 2015, 37,332 performance-contingent cash awards granted in 2013 vested, resulting in cash payouts valued at $2.4 million.
WPL [Member] |
Benefit Plans | BENEFIT PLANS NOTE 9(a) Pension and Other Postretirement Benefits Plans - Net Periodic Benefit Costs (Credits) - The components of net periodic benefit costs (credits) for sponsored defined benefit pension and OPEB plans for the three months ended March 31 are included in the tables below (in millions). In IPL’s and WPL’s tables below, the defined benefit pension plans costs represent those respective costs for their bargaining unit employees covered under the qualified plans that they sponsor, as well as amounts directly assigned to them related to their current and former non-bargaining employees who are participants in the Alliant Energy and Corporate Services sponsored qualified and non-qualified defined benefit pension plans. In IPL’s and WPL’s tables below, the OPEB plans costs (credits) represent respective costs (credits) for their employees, as well as amounts directly assigned to them related to their current and former non-bargaining employees who are participants in the Corporate Services sponsored OPEB plan.
| Defined Benefit Pension Plans |  | OPEB Plans
Alliant Energy | 2016 |  | 2015 |  | 2016 |  | 2015
Service cost |  | $3.2 |  |  |  | $4.0 |  |  |  | $1.3 |  |  |  | $1.4 |
Interest cost | 13.3 |  |  | 13.4 |  |  | 2.3 |  |  | 2.2 |
Expected return on plan assets | (16.4 | ) |  | (18.7 | ) |  | (1.5 | ) |  | (2.1 | )
Amortization of prior service credit | (0.1 | ) |  | (0.1 | ) |  | (1.0 | ) |  | (2.8 | )
Amortization of actuarial loss | 9.3 |  |  | 8.8 |  |  | 1.2 |  |  | 1.2 |
Additional benefit costs | — |  |  | 0.2 |  |  | — |  |  | — |
|  | $9.3 |  |  |  | $7.6 |  |  |  | $2.3 |  |  |  | ($0.1 | )
| Defined Benefit Pension Plans |  | OPEB Plans
IPL | 2016 |  | 2015 |  | 2016 |  | 2015
Service cost |  | $1.9 |  |  |  | $2.2 |  |  |  | $0.6 |  |  |  | $0.6 |
Interest cost | 6.1 |  |  | 6.2 |  |  | 1.0 |  |  | 0.9 |
Expected return on plan assets | (7.7 | ) |  | (8.9 | ) |  | (1.0 | ) |  | (1.4 | )
Amortization of prior service credit | — |  |  | — |  |  | (0.7 | ) |  | (1.5 | )
Amortization of actuarial loss | 4.1 |  |  | 3.8 |  |  | 0.6 |  |  | 0.6 |
|  | $4.4 |  |  |  | $3.3 |  |  |  | $0.5 |  |  |  | ($0.8 | )
| Defined Benefit Pension Plans |  | OPEB Plans
WPL | 2016 |  | 2015 |  | 2016 |  | 2015
Service cost |  | $1.2 |  |  |  | $1.4 |  |  |  | $0.5 |  |  |  | $0.6 |
Interest cost | 5.6 |  |  | 5.6 |  |  | 0.9 |  |  | 0.9 |
Expected return on plan assets | (7.1 | ) |  | (8.1 | ) |  | (0.2 | ) |  | (0.4 | )
Amortization of prior service cost (credit) | 0.1 |  |  | 0.1 |  |  | (0.2 | ) |  | (0.9 | )
Amortization of actuarial loss | 4.4 |  |  | 4.2 |  |  | 0.5 |  |  | 0.6 |
Additional benefit costs | — |  |  | 0.2 |  |  | — |  |  | — |
|  | $4.2 |  |  |  | $3.4 |  |  |  | $1.5 |  |  |  | $0.8 |
401(k) Savings Plans - A significant number of employees participate in defined contribution retirement plans (401(k) savings plans). For the three months ended March 31, costs related to the 401(k) savings plans, which are partially based on the participants’ contributions and include allocated costs associated with Corporate Services employees for IPL and WPL, were as follows (in millions):
| Alliant Energy |  | IPL |  | WPL
| 2016 |  | 2015 |  | 2016 |  | 2015 |  | 2016 |  | 2015
401(k) costs |  | $6.2 |  |  |  | $6.7 |  |  |  | $3.1 |  |  |  | $3.4 |  |  |  | $2.8 |  |  |  | $2.9 |
NOTE 9(b) Equity-based Compensation Plans - 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 months ended March 31 was as follows (in millions):
| Alliant Energy |  | IPL |  | WPL
| 2016 |  | 2015 |  | 2016 |  | 2015 |  | 2016 |  | 2015
Compensation expense |  | $5.3 |  |  |  | $3.2 |  |  |  | $2.8 |  |  |  | $1.7 |  |  |  | $2.3 |  |  |  | $1.4 |
Income tax benefits | 2.2 |  |  | 1.3 |  |  | 1.1 |  |  | 0.7 |  |  | 0.9 |  |  | 0.6 |
As of March 31, 2016, total unrecognized compensation cost related to share-based compensation awards was $12.9 million, which is expected to be recognized over a weighted average period of between one and two years. Share-based compensation expense is recognized on a straight-line basis over the requisite service periods and is primarily recorded in “Other operation and maintenance” in the income statements. Performance Shares and Performance Units - A summary of the performance shares and performance units activity, with amounts representing the target number of awards, was as follows:
| Performance Shares |  | Performance Units
| 2016 |  | 2015 |  | 2016 |  | 2015
Nonvested awards, January 1 | 144,215 |  |  | 144,424 |  |  | 58,206 |  |  | 63,665 |
Granted | 33,776 |  |  | 45,403 |  |  | 11,959 |  |  | 17,837 |
Vested | (49,093 | ) |  | (45,612 | ) |  | (21,380 | ) |  | (22,845 | )
Forfeited | (615 | ) |  | — |  |  | (382 | ) |  | (93 | )
Nonvested awards, March 31 | 128,283 |  |  | 144,215 |  |  | 48,403 |  |  | 58,564 |
Granted Awards - For the performance units granted in 2016, each performance unit’s value is based on the closing market price of one share of Alliant Energy’s common stock at the end of the performance period. For the performance units granted prior to 2016, each performance unit’s value is based on the closing market price of one share of Alliant Energy’s common stock on the grant date of the award. Vested Awards - During the three months ended March 31, certain performance shares and performance units vested, resulting in payouts (a combination of cash and common stock for the performance shares and cash only for the performance units) as follows:
| Performance Shares |  | Performance Units
| 2016 |  | 2015 |  | 2016 |  | 2015
| 2013 Grant |  | 2012 Grant |  | 2013 Grant |  | 2012 Grant
Performance awards vested | 49,093 |  |  | 45,612 |  |  | 21,380 |  |  | 22,845 |
Percentage of target number of performance awards | 165.0 | % |  | 167.5 | % |  | 165.0 | % |  | 167.5 | %
Aggregate payout value (in millions) |  | $5.1 |  |  |  | $5.1 |  |  |  | $1.7 |  |  |  | $1.6 |
Payout - cash (in millions) |  | $2.9 |  |  |  | $3.2 |  |  |  | $1.7 |  |  |  | $1.6 |
Payout - common stock shares issued | 11,204 |  |  | 10,975 |  |  | N/A |  | N/A
Fair Value of Awards - Information related to fair values of nonvested performance shares and performance units at March 31, 2016, by year of grant, was as follows:
| Performance Shares |  | Performance Units
| 2016 Grant |  | 2015 Grant |  | 2014 Grant |  | 2016 Grant |  | 2015 Grant |  | 2014 Grant
Nonvested awards | 33,161 |  |  | 45,403 |  |  | 49,719 |  |  | 11,959 |  |  | 17,209 |  |  | 19,235 |
Alliant Energy common stock closing price on March 31, 2016 |  | $74.28 |  |  |  | $74.28 |  |  |  | $74.28 |  |  |  | $74.28 |  |  | N/A |  | N/A
Alliant Energy common stock closing price on grant date | N/A |  | N/A |  | N/A |  | N/A |  |  | $65.09 |  |  |  | $53.77 |
Estimated payout percentage based on performance criteria | 108 | % |  | 90 | % |  | 138 | % |  | 108 | % |  | 90 | % |  | 138 | %
Fair values of each nonvested award |  | $80.22 |  |  |  | $66.85 |  |  |  | $102.51 |  |  |  | $80.22 |  |  |  | $58.58 |  |  |  | $74.20 |
At March 31, 2016, fair values of nonvested performance shares and performance units were calculated based on Alliant Energy’s stock price and anticipated total shareowner returns of Alliant Energy and its investor-owned utility peer group over the performance period. The portion of the fair values based on anticipated total shareowner returns was estimated using a model that incorporates the probability of meeting performance targets based on historical returns relative to the peer group. Performance Contingent Restricted Stock - A summary of the performance contingent restricted stock activity was as follows:
| 2016 |  | 2015
| Shares |  | Weighted Average Grant Date Fair Value |  | Shares |  | Weighted Average Grant Date Fair Value
Nonvested shares, January 1 | 95,122 |  |  |  | $59.17 |  |  | 98,812 |  |  |  | $50.69 |
Granted | — |  |  | — |  |  | 45,403 |  |  | 65.09 |
Vested (a) | — |  |  | — |  |  | (49,093 | ) |  | 47.58 |
Nonvested shares, March 31 | 95,122 |  |  | 59.17 |  |  | 95,122 |  |  | 59.17 |
(a) | In 2015, 49,093 performance contingent restricted shares granted in 2013 vested because the specified performance criteria for such shares were met.
Performance Restricted Stock Units and Performance Restricted Units - Alliant Energy granted new types of share-based compensation awards to key employees in the first quarter of 2016 referred to as performance restricted stock units, performance restricted units and key employee performance restricted units. Payouts of these units are based on the achievement of certain performance targets (currently specified growth of consolidated income from continuing operations) during the three-year performance period. The actual number of units that will be paid out upon vesting is dependent upon actual performance and may range from zero to 200% of the target number of units. If performance targets are not met during the performance period, these units are forfeited. Subject to achievement of the performance criteria, payouts of nonvested units are prorated in the event of retirement, death or disability during the first year of the performance period based on time worked during the first year of the period, and are prorated upon involuntary termination without cause based on time worked during the entire period. Subject to achievement of the performance criteria, payouts of units to participants who terminate employment after the first year of the performance period due to retirement, death or disability are not prorated. Participants’ nonvested units are forfeited if the participant voluntarily leaves Alliant Energy or is terminated for cause during the performance period. Performance Restricted Stock Units - Performance restricted stock units must be paid out in shares and are accounted for as equity awards. Each performance restricted stock unit’s value is based on the closing market price of one share of Alliant Energy’s common stock on the grant date of the award. A summary of the performance restricted stock units activity, with amounts representing the target number of units, was as follows:
| 2016
| Units |  | Weighted Average Grant Date Fair Value
Granted | 33,776 |  |  |  | $67.85 |
Forfeited | (615 | ) |  | 67.80 |
Nonvested units, March 31 | 33,161 |  |  | 67.85 |
Performance Restricted Units - Performance restricted units must be paid out in cash and are accounted for as liability awards. Each performance restricted unit’s value is based on the closing market price of one share of Alliant Energy’s common stock at the end of the performance period. A summary of the performance restricted units activity, with amounts representing the target number of units, was as follows:
| 2016
Granted | 11,959 |
Nonvested units, March 31 | 11,959 |
Key Employee Performance Restricted Units - Key employee performance restricted units must be paid out in cash and are accounted for as liability awards. Each key employee performance restricted unit’s value is based on the closing market price of one share of Alliant Energy’s common stock on the grant date of the award. A summary of the key employee performance restricted units activity, with amounts representing the target number of units, was as follows:
| 2016
| Units |  | Weighted Average Grant Date Fair Value
Granted | 22,528 |  |  |  | $67.80 |
Nonvested units, March 31 | 22,528 |  |  | 67.80 |
Restricted Stock Units and Restricted Units - Alliant Energy granted new types of share-based compensation awards to key employees in the first quarter of 2016 referred to as restricted stock units and restricted units. Payouts of these units are based on the expiration of a three-year time-vesting period. Payouts of nonvested units are prorated in the event of retirement, death or disability during the first year of the time-vesting period based on time worked during the first year of the period, and are prorated upon involuntary termination without cause based on time worked during the entire period. Upon expiration of the time-vesting period, payouts of units to participants who terminate employment after the first year of the period due to retirement, death or disability are not prorated. Participants’ nonvested units are forfeited if the participant voluntarily leaves Alliant Energy or is terminated for cause during the time-vesting period. Each restricted stock unit’s and restricted unit’s value is based on the closing market price of one share of Alliant Energy’s common stock at the end of the time-vesting period. Restricted stock units can be paid out in shares of Alliant Energy common stock, cash or a combination of cash and stock. Restricted units must be paid out in cash. Alliant Energy assumes it will make future payouts of its restricted stock units and restricted units in cash; therefore, restricted stock units and restricted units are accounted for as liability awards. A summary of the restricted stock units and restricted units activity was as follows:
| 2016
| Restricted Stock Units |  | Restricted Units
Granted | 28,952 |  |  | 10,251 |
Forfeited | (527 | ) |  | — |
Nonvested units, March 31 | 28,425 |  |  | 10,251 |
Performance-Contingent Cash Awards - A summary of the performance-contingent cash awards activity was as follows:
| 2016 |  | 2015
Nonvested awards, January 1 | 81,876 |  |  | 78,930 |
Granted | — |  |  | 41,105 |
Vested (a) | — |  |  | (37,332 | )
Forfeited | (382 | ) |  | (469 | )
Nonvested awards, March 31 | 81,494 |  |  | 82,234 |
(a) | In 2015, 37,332 performance-contingent cash awards granted in 2013 vested, resulting in cash payouts valued at $2.4 million.

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