XML 37 R14.htm IDEA: XBRL DOCUMENT
v3.7.0.1

Benefit Plans | 3 Months Ended
--- | ---
Mar. 31, 2017
Benefit Plans | BENEFIT PLANS NOTE 9(a) Pension and Other Postretirement Benefits Plans - Net Periodic Benefit Costs - The components of net periodic benefit costs 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 amounts represent those respective amounts 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 amounts represent respective amounts 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 | 2017 |  | 2016 |  | 2017 |  | 2016
Service cost |  | $3.1 |  |  |  | $3.2 |  |  |  | $1.2 |  |  |  | $1.3 |
Interest cost | 12.8 |  |  | 13.3 |  |  | 2.2 |  |  | 2.3 |
Expected return on plan assets | (16.4 | ) |  | (16.4 | ) |  | (1.5 | ) |  | (1.5 | )
Amortization of prior service credit | (0.1 | ) |  | (0.1 | ) |  | (0.1 | ) |  | (1.0 | )
Amortization of actuarial loss | 9.4 |  |  | 9.3 |  |  | 1.0 |  |  | 1.2 |
|  | $8.8 |  |  |  | $9.3 |  |  |  | $2.8 |  |  |  | $2.3 |
| Defined Benefit Pension Plans |  | OPEB Plans
IPL | 2017 |  | 2016 |  | 2017 |  | 2016
Service cost |  | $1.8 |  |  |  | $1.9 |  |  |  | $0.5 |  |  |  | $0.6 |
Interest cost | 5.9 |  |  | 6.1 |  |  | 0.9 |  |  | 1.0 |
Expected return on plan assets | (7.7 | ) |  | (7.7 | ) |  | (1.1 | ) |  | (1.0 | )
Amortization of prior service credit | — |  |  | — |  |  | — |  |  | (0.7 | )
Amortization of actuarial loss | 4.0 |  |  | 4.1 |  |  | 0.5 |  |  | 0.6 |
|  | $4.0 |  |  |  | $4.4 |  |  |  | $0.8 |  |  |  | $0.5 |
| Defined Benefit Pension Plans |  | OPEB Plans
WPL | 2017 |  | 2016 |  | 2017 |  | 2016
Service cost |  | $1.2 |  |  |  | $1.2 |  |  |  | $0.5 |  |  |  | $0.5 |
Interest cost | 5.5 |  |  | 5.6 |  |  | 0.9 |  |  | 0.9 |
Expected return on plan assets | (7.1 | ) |  | (7.1 | ) |  | (0.2 | ) |  | (0.2 | )
Amortization of prior service cost (credit) | — |  |  | 0.1 |  |  | (0.1 | ) |  | (0.2 | )
Amortization of actuarial loss | 4.6 |  |  | 4.4 |  |  | 0.4 |  |  | 0.5 |
|  | $4.2 |  |  |  | $4.2 |  |  |  | $1.5 |  |  |  | $1.5 |
401(k) Savings Plan - A significant number of employees participate in a defined contribution retirement plan (401(k) savings plan). For the three months ended March 31, costs related to the 401(k) savings plan, 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
| 2017 |  | 2016 |  | 2017 |  | 2016 |  | 2017 |  | 2016
401(k) costs |  | $6.5 |  |  |  | $6.2 |  |  |  | $3.4 |  |  |  | $3.1 |  |  |  | $2.9 |  |  |  | $2.8 |
NOTE 9(b) Equity-based Compensation Plans - All shares, units and awards included below have been adjusted to reflect the common stock split distributed in May 2016. 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
| 2017 |  | 2016 |  | 2017 |  | 2016 |  | 2017 |  | 2016
Compensation expense |  | $3.2 |  |  |  | $5.3 |  |  |  | $1.7 |  |  |  | $2.8 |  |  |  | $1.4 |  |  |  | $2.3 |
Income tax benefits | 1.3 |  |  | 2.2 |  |  | 0.7 |  |  | 1.1 |  |  | 0.5 |  |  | 0.9 |
As of March 31, 2017, Alliant Energy’s, IPL’s and WPL’s total unrecognized compensation cost related to share-based compensation awards was $14.0 million, $7.6 million and $5.9 million, which is expected to be recognized over a weighted average period of between one and two years. 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
| 2017 |  | 2016 |  | 2017 |  | 2016
Nonvested awards, January 1 | 257,599 |  |  | 288,430 |  |  | 93,320 |  |  | 116,412 |
Granted | 63,804 |  |  | 67,552 |  |  | 21,558 |  |  | 23,918 |
Vested | (99,438 | ) |  | (98,186 | ) |  | (37,395 | ) |  | (42,760 | )
Forfeited | — |  |  | (1,230 | ) |  | (497 | ) |  | (764 | )
Nonvested awards, March 31 | 221,965 |  |  | 256,566 |  |  | 76,986 |  |  | 96,806 |
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
| 2017 |  | 2016 |  | 2017 |  | 2016
| 2014 Grant |  | 2013 Grant |  | 2014 Grant |  | 2013 Grant
Performance awards vested | 99,438 |  |  | 98,186 |  |  | 37,395 |  |  | 42,760 |
Percentage of target number of performance awards | 147.5 | % |  | 165.0 | % |  | 147.5 | % |  | 165.0 | %
Aggregate payout value (in millions) |  | $5.6 |  |  |  | $5.1 |  |  |  | $1.5 |  |  |  | $1.7 |
Payout - cash (in millions) |  | $5.1 |  |  |  | $2.9 |  |  |  | $1.5 |  |  |  | $1.7 |
Payout - common stock shares issued | 5,185 |  |  | 22,408 |  |  | N/A |  | N/A
Fair Value of Awards - Information related to fair values of nonvested performance shares and performance units at March 31, 2017, by year of grant, was as follows:
| Performance Shares |  | Performance Units
| 2017 Grant |  | 2016 Grant |  | 2015 Grant |  | 2017 Grant |  | 2016 Grant |  | 2015 Grant
Nonvested awards at target | 63,804 |  |  | 67,355 |  |  | 90,806 |  |  | 21,061 |  |  | 22,657 |  |  | 33,268 |
Alliant Energy common stock closing price on March 31, 2017 |  | $39.61 |  |  |  | $39.61 |  |  |  | $39.61 |  |  |  | $39.61 |  |  |  | $39.61 |  |  | N/A
Alliant Energy common stock closing price on grant date | N/A |  | N/A |  | N/A |  | N/A |  | N/A |  |  | $32.55 |
Estimated payout percentage based on performance criteria | 100 | % |  | 160 | % |  | 130 | % |  | 100 | % |  | 160 | % |  | 130 | %
Fair values of each nonvested award |  | $39.61 |  |  |  | $63.38 |  |  |  | $51.49 |  |  |  | $39.61 |  |  |  | $63.38 |  |  |  | $42.32 |
Performance-Contingent Restricted Stock - Alliant Energy has not granted any performance-contingent restricted stock since 2015. In 2017, 99,438 performance-contingent restricted shares granted in 2014 vested because the specified performance criteria for such shares were met. There were 90,806 shares of nonvested performance-contingent restricted stock outstanding at March 31, 2017, with a weighted average grant date fair value of $32.55. Performance Restricted Stock Units - A summary of the performance restricted stock units activity, with amounts representing the target number of units, was as follows:
| 2017 |  | 2016
| Units |  | Weighted Average Grant Date Fair Value |  | Units |  | Weighted Average Grant Date Fair Value
Nonvested units, January 1 | 67,355 |  |  |  | $33.96 |  |  | — |  |  |  | $— |
Granted | 63,804 |  |  | 39.11 |  |  | 67,552 |  |  | 33.93 |
Forfeited | — |  |  | — |  |  | (1,230 | ) |  | 33.90 |
Nonvested units, March 31 | 131,159 |  |  | 36.46 |  |  | 66,322 |  |  | 33.93 |
Restricted Stock Units - A summary of the restricted stock units activity was as follows:
| 2017 |  | 2016
Nonvested units, January 1 | 57,736 |  |  | — |
Granted | 54,688 |  |  | 57,904 |
Forfeited | — |  |  | (1,054 | )
Nonvested units, March 31 | 112,424 |  |  | 56,850 |
Performance-Contingent Cash Awards - Alliant Energy has not granted any performance-contingent cash awards since 2015. In 2017, 79,719 performance-contingent cash awards granted in 2014 vested, resulting in cash payouts valued at $3.1 million. There were 79,616 shares of nonvested performance-contingent cash awards outstanding at March 31, 2017.
IPL [Member] |
Benefit Plans | BENEFIT PLANS NOTE 9(a) Pension and Other Postretirement Benefits Plans - Net Periodic Benefit Costs - The components of net periodic benefit costs 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 amounts represent those respective amounts 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 amounts represent respective amounts 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 | 2017 |  | 2016 |  | 2017 |  | 2016
Service cost |  | $3.1 |  |  |  | $3.2 |  |  |  | $1.2 |  |  |  | $1.3 |
Interest cost | 12.8 |  |  | 13.3 |  |  | 2.2 |  |  | 2.3 |
Expected return on plan assets | (16.4 | ) |  | (16.4 | ) |  | (1.5 | ) |  | (1.5 | )
Amortization of prior service credit | (0.1 | ) |  | (0.1 | ) |  | (0.1 | ) |  | (1.0 | )
Amortization of actuarial loss | 9.4 |  |  | 9.3 |  |  | 1.0 |  |  | 1.2 |
|  | $8.8 |  |  |  | $9.3 |  |  |  | $2.8 |  |  |  | $2.3 |
| Defined Benefit Pension Plans |  | OPEB Plans
IPL | 2017 |  | 2016 |  | 2017 |  | 2016
Service cost |  | $1.8 |  |  |  | $1.9 |  |  |  | $0.5 |  |  |  | $0.6 |
Interest cost | 5.9 |  |  | 6.1 |  |  | 0.9 |  |  | 1.0 |
Expected return on plan assets | (7.7 | ) |  | (7.7 | ) |  | (1.1 | ) |  | (1.0 | )
Amortization of prior service credit | — |  |  | — |  |  | — |  |  | (0.7 | )
Amortization of actuarial loss | 4.0 |  |  | 4.1 |  |  | 0.5 |  |  | 0.6 |
|  | $4.0 |  |  |  | $4.4 |  |  |  | $0.8 |  |  |  | $0.5 |
| Defined Benefit Pension Plans |  | OPEB Plans
WPL | 2017 |  | 2016 |  | 2017 |  | 2016
Service cost |  | $1.2 |  |  |  | $1.2 |  |  |  | $0.5 |  |  |  | $0.5 |
Interest cost | 5.5 |  |  | 5.6 |  |  | 0.9 |  |  | 0.9 |
Expected return on plan assets | (7.1 | ) |  | (7.1 | ) |  | (0.2 | ) |  | (0.2 | )
Amortization of prior service cost (credit) | — |  |  | 0.1 |  |  | (0.1 | ) |  | (0.2 | )
Amortization of actuarial loss | 4.6 |  |  | 4.4 |  |  | 0.4 |  |  | 0.5 |
|  | $4.2 |  |  |  | $4.2 |  |  |  | $1.5 |  |  |  | $1.5 |
401(k) Savings Plan - A significant number of employees participate in a defined contribution retirement plan (401(k) savings plan). For the three months ended March 31, costs related to the 401(k) savings plan, 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
| 2017 |  | 2016 |  | 2017 |  | 2016 |  | 2017 |  | 2016
401(k) costs |  | $6.5 |  |  |  | $6.2 |  |  |  | $3.4 |  |  |  | $3.1 |  |  |  | $2.9 |  |  |  | $2.8 |
NOTE 9(b) Equity-based Compensation Plans - All shares, units and awards included below have been adjusted to reflect the common stock split distributed in May 2016. 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
| 2017 |  | 2016 |  | 2017 |  | 2016 |  | 2017 |  | 2016
Compensation expense |  | $3.2 |  |  |  | $5.3 |  |  |  | $1.7 |  |  |  | $2.8 |  |  |  | $1.4 |  |  |  | $2.3 |
Income tax benefits | 1.3 |  |  | 2.2 |  |  | 0.7 |  |  | 1.1 |  |  | 0.5 |  |  | 0.9 |
As of March 31, 2017, Alliant Energy’s, IPL’s and WPL’s total unrecognized compensation cost related to share-based compensation awards was $14.0 million, $7.6 million and $5.9 million, which is expected to be recognized over a weighted average period of between one and two years. 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
| 2017 |  | 2016 |  | 2017 |  | 2016
Nonvested awards, January 1 | 257,599 |  |  | 288,430 |  |  | 93,320 |  |  | 116,412 |
Granted | 63,804 |  |  | 67,552 |  |  | 21,558 |  |  | 23,918 |
Vested | (99,438 | ) |  | (98,186 | ) |  | (37,395 | ) |  | (42,760 | )
Forfeited | — |  |  | (1,230 | ) |  | (497 | ) |  | (764 | )
Nonvested awards, March 31 | 221,965 |  |  | 256,566 |  |  | 76,986 |  |  | 96,806 |
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
| 2017 |  | 2016 |  | 2017 |  | 2016
| 2014 Grant |  | 2013 Grant |  | 2014 Grant |  | 2013 Grant
Performance awards vested | 99,438 |  |  | 98,186 |  |  | 37,395 |  |  | 42,760 |
Percentage of target number of performance awards | 147.5 | % |  | 165.0 | % |  | 147.5 | % |  | 165.0 | %
Aggregate payout value (in millions) |  | $5.6 |  |  |  | $5.1 |  |  |  | $1.5 |  |  |  | $1.7 |
Payout - cash (in millions) |  | $5.1 |  |  |  | $2.9 |  |  |  | $1.5 |  |  |  | $1.7 |
Payout - common stock shares issued | 5,185 |  |  | 22,408 |  |  | N/A |  | N/A
Fair Value of Awards - Information related to fair values of nonvested performance shares and performance units at March 31, 2017, by year of grant, was as follows:
| Performance Shares |  | Performance Units
| 2017 Grant |  | 2016 Grant |  | 2015 Grant |  | 2017 Grant |  | 2016 Grant |  | 2015 Grant
Nonvested awards at target | 63,804 |  |  | 67,355 |  |  | 90,806 |  |  | 21,061 |  |  | 22,657 |  |  | 33,268 |
Alliant Energy common stock closing price on March 31, 2017 |  | $39.61 |  |  |  | $39.61 |  |  |  | $39.61 |  |  |  | $39.61 |  |  |  | $39.61 |  |  | N/A
Alliant Energy common stock closing price on grant date | N/A |  | N/A |  | N/A |  | N/A |  | N/A |  |  | $32.55 |
Estimated payout percentage based on performance criteria | 100 | % |  | 160 | % |  | 130 | % |  | 100 | % |  | 160 | % |  | 130 | %
Fair values of each nonvested award |  | $39.61 |  |  |  | $63.38 |  |  |  | $51.49 |  |  |  | $39.61 |  |  |  | $63.38 |  |  |  | $42.32 |
Performance-Contingent Restricted Stock - Alliant Energy has not granted any performance-contingent restricted stock since 2015. In 2017, 99,438 performance-contingent restricted shares granted in 2014 vested because the specified performance criteria for such shares were met. There were 90,806 shares of nonvested performance-contingent restricted stock outstanding at March 31, 2017, with a weighted average grant date fair value of $32.55. Performance Restricted Stock Units - A summary of the performance restricted stock units activity, with amounts representing the target number of units, was as follows:
| 2017 |  | 2016
| Units |  | Weighted Average Grant Date Fair Value |  | Units |  | Weighted Average Grant Date Fair Value
Nonvested units, January 1 | 67,355 |  |  |  | $33.96 |  |  | — |  |  |  | $— |
Granted | 63,804 |  |  | 39.11 |  |  | 67,552 |  |  | 33.93 |
Forfeited | — |  |  | — |  |  | (1,230 | ) |  | 33.90 |
Nonvested units, March 31 | 131,159 |  |  | 36.46 |  |  | 66,322 |  |  | 33.93 |
Restricted Stock Units - A summary of the restricted stock units activity was as follows:
| 2017 |  | 2016
Nonvested units, January 1 | 57,736 |  |  | — |
Granted | 54,688 |  |  | 57,904 |
Forfeited | — |  |  | (1,054 | )
Nonvested units, March 31 | 112,424 |  |  | 56,850 |
Performance-Contingent Cash Awards - Alliant Energy has not granted any performance-contingent cash awards since 2015. In 2017, 79,719 performance-contingent cash awards granted in 2014 vested, resulting in cash payouts valued at $3.1 million. There were 79,616 shares of nonvested performance-contingent cash awards outstanding at March 31, 2017.
WPL [Member] |
Benefit Plans | BENEFIT PLANS NOTE 9(a) Pension and Other Postretirement Benefits Plans - Net Periodic Benefit Costs - The components of net periodic benefit costs 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 amounts represent those respective amounts 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 amounts represent respective amounts 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 | 2017 |  | 2016 |  | 2017 |  | 2016
Service cost |  | $3.1 |  |  |  | $3.2 |  |  |  | $1.2 |  |  |  | $1.3 |
Interest cost | 12.8 |  |  | 13.3 |  |  | 2.2 |  |  | 2.3 |
Expected return on plan assets | (16.4 | ) |  | (16.4 | ) |  | (1.5 | ) |  | (1.5 | )
Amortization of prior service credit | (0.1 | ) |  | (0.1 | ) |  | (0.1 | ) |  | (1.0 | )
Amortization of actuarial loss | 9.4 |  |  | 9.3 |  |  | 1.0 |  |  | 1.2 |
|  | $8.8 |  |  |  | $9.3 |  |  |  | $2.8 |  |  |  | $2.3 |
| Defined Benefit Pension Plans |  | OPEB Plans
IPL | 2017 |  | 2016 |  | 2017 |  | 2016
Service cost |  | $1.8 |  |  |  | $1.9 |  |  |  | $0.5 |  |  |  | $0.6 |
Interest cost | 5.9 |  |  | 6.1 |  |  | 0.9 |  |  | 1.0 |
Expected return on plan assets | (7.7 | ) |  | (7.7 | ) |  | (1.1 | ) |  | (1.0 | )
Amortization of prior service credit | — |  |  | — |  |  | — |  |  | (0.7 | )
Amortization of actuarial loss | 4.0 |  |  | 4.1 |  |  | 0.5 |  |  | 0.6 |
|  | $4.0 |  |  |  | $4.4 |  |  |  | $0.8 |  |  |  | $0.5 |
| Defined Benefit Pension Plans |  | OPEB Plans
WPL | 2017 |  | 2016 |  | 2017 |  | 2016
Service cost |  | $1.2 |  |  |  | $1.2 |  |  |  | $0.5 |  |  |  | $0.5 |
Interest cost | 5.5 |  |  | 5.6 |  |  | 0.9 |  |  | 0.9 |
Expected return on plan assets | (7.1 | ) |  | (7.1 | ) |  | (0.2 | ) |  | (0.2 | )
Amortization of prior service cost (credit) | — |  |  | 0.1 |  |  | (0.1 | ) |  | (0.2 | )
Amortization of actuarial loss | 4.6 |  |  | 4.4 |  |  | 0.4 |  |  | 0.5 |
|  | $4.2 |  |  |  | $4.2 |  |  |  | $1.5 |  |  |  | $1.5 |
401(k) Savings Plan - A significant number of employees participate in a defined contribution retirement plan (401(k) savings plan). For the three months ended March 31, costs related to the 401(k) savings plan, 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
| 2017 |  | 2016 |  | 2017 |  | 2016 |  | 2017 |  | 2016
401(k) costs |  | $6.5 |  |  |  | $6.2 |  |  |  | $3.4 |  |  |  | $3.1 |  |  |  | $2.9 |  |  |  | $2.8 |
NOTE 9(b) Equity-based Compensation Plans - All shares, units and awards included below have been adjusted to reflect the common stock split distributed in May 2016. 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
| 2017 |  | 2016 |  | 2017 |  | 2016 |  | 2017 |  | 2016
Compensation expense |  | $3.2 |  |  |  | $5.3 |  |  |  | $1.7 |  |  |  | $2.8 |  |  |  | $1.4 |  |  |  | $2.3 |
Income tax benefits | 1.3 |  |  | 2.2 |  |  | 0.7 |  |  | 1.1 |  |  | 0.5 |  |  | 0.9 |
As of March 31, 2017, Alliant Energy’s, IPL’s and WPL’s total unrecognized compensation cost related to share-based compensation awards was $14.0 million, $7.6 million and $5.9 million, which is expected to be recognized over a weighted average period of between one and two years. 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
| 2017 |  | 2016 |  | 2017 |  | 2016
Nonvested awards, January 1 | 257,599 |  |  | 288,430 |  |  | 93,320 |  |  | 116,412 |
Granted | 63,804 |  |  | 67,552 |  |  | 21,558 |  |  | 23,918 |
Vested | (99,438 | ) |  | (98,186 | ) |  | (37,395 | ) |  | (42,760 | )
Forfeited | — |  |  | (1,230 | ) |  | (497 | ) |  | (764 | )
Nonvested awards, March 31 | 221,965 |  |  | 256,566 |  |  | 76,986 |  |  | 96,806 |
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
| 2017 |  | 2016 |  | 2017 |  | 2016
| 2014 Grant |  | 2013 Grant |  | 2014 Grant |  | 2013 Grant
Performance awards vested | 99,438 |  |  | 98,186 |  |  | 37,395 |  |  | 42,760 |
Percentage of target number of performance awards | 147.5 | % |  | 165.0 | % |  | 147.5 | % |  | 165.0 | %
Aggregate payout value (in millions) |  | $5.6 |  |  |  | $5.1 |  |  |  | $1.5 |  |  |  | $1.7 |
Payout - cash (in millions) |  | $5.1 |  |  |  | $2.9 |  |  |  | $1.5 |  |  |  | $1.7 |
Payout - common stock shares issued | 5,185 |  |  | 22,408 |  |  | N/A |  | N/A
Fair Value of Awards - Information related to fair values of nonvested performance shares and performance units at March 31, 2017, by year of grant, was as follows:
| Performance Shares |  | Performance Units
| 2017 Grant |  | 2016 Grant |  | 2015 Grant |  | 2017 Grant |  | 2016 Grant |  | 2015 Grant
Nonvested awards at target | 63,804 |  |  | 67,355 |  |  | 90,806 |  |  | 21,061 |  |  | 22,657 |  |  | 33,268 |
Alliant Energy common stock closing price on March 31, 2017 |  | $39.61 |  |  |  | $39.61 |  |  |  | $39.61 |  |  |  | $39.61 |  |  |  | $39.61 |  |  | N/A
Alliant Energy common stock closing price on grant date | N/A |  | N/A |  | N/A |  | N/A |  | N/A |  |  | $32.55 |
Estimated payout percentage based on performance criteria | 100 | % |  | 160 | % |  | 130 | % |  | 100 | % |  | 160 | % |  | 130 | %
Fair values of each nonvested award |  | $39.61 |  |  |  | $63.38 |  |  |  | $51.49 |  |  |  | $39.61 |  |  |  | $63.38 |  |  |  | $42.32 |
Performance-Contingent Restricted Stock - Alliant Energy has not granted any performance-contingent restricted stock since 2015. In 2017, 99,438 performance-contingent restricted shares granted in 2014 vested because the specified performance criteria for such shares were met. There were 90,806 shares of nonvested performance-contingent restricted stock outstanding at March 31, 2017, with a weighted average grant date fair value of $32.55. Performance Restricted Stock Units - A summary of the performance restricted stock units activity, with amounts representing the target number of units, was as follows:
| 2017 |  | 2016
| Units |  | Weighted Average Grant Date Fair Value |  | Units |  | Weighted Average Grant Date Fair Value
Nonvested units, January 1 | 67,355 |  |  |  | $33.96 |  |  | — |  |  |  | $— |
Granted | 63,804 |  |  | 39.11 |  |  | 67,552 |  |  | 33.93 |
Forfeited | — |  |  | — |  |  | (1,230 | ) |  | 33.90 |
Nonvested units, March 31 | 131,159 |  |  | 36.46 |  |  | 66,322 |  |  | 33.93 |
Restricted Stock Units - A summary of the restricted stock units activity was as follows:
| 2017 |  | 2016
Nonvested units, January 1 | 57,736 |  |  | — |
Granted | 54,688 |  |  | 57,904 |
Forfeited | — |  |  | (1,054 | )
Nonvested units, March 31 | 112,424 |  |  | 56,850 |
Performance-Contingent Cash Awards - Alliant Energy has not granted any performance-contingent cash awards since 2015. In 2017, 79,719 performance-contingent cash awards granted in 2014 vested, resulting in cash payouts valued at $3.1 million. There were 79,616 shares of nonvested performance-contingent cash awards outstanding at March 31, 2017.

X
- Definition The entire disclosure for an entity's employee compensation and benefit plans, including, but not limited to, postemployment and postretirement benefit plans, defined benefit pension plans, defined contribution plans, non-qualified and supplemental benefit plans, deferred compensation, share-based compensation, life insurance, severance, health care, unemployment and other benefit plans. + References No definition available. + Details
Name: | us-gaap_CompensationAndEmployeeBenefitPlansTextBlock
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: |