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Benefit Plans (Tables) | 12 Months Ended
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Dec. 31, 2017
Defined Benefit Plan Disclosure [Line Items] |
Assumptions Used To Measure Benefit Plans | The assumptions for defined benefit pension and OPEB plans at the measurement date of December 31 were as follows:
| Defined Benefit Pension Plans |  | OPEB Plans
Alliant Energy | 2017 |  | 2016 |  | 2015 |  | 2017 |  | 2016 |  | 2015
Discount rate for benefit obligations | 3.66% |  | 4.19% |  | 4.47% |  | 3.53% |  | 3.98% |  | 4.30%
Discount rate for net periodic cost | 4.19% |  | 4.47% |  | 4.18% |  | 3.98% |  | 4.30% |  | 3.97%
Expected rate of return on plan assets | 7.60% |  | 7.60% |  | 7.60% |  | 5.80% |  | 6.30% |  | 6.20%
Rate of compensation increase | 3.65 | % | - | 4.50% |  | 3.65 | % | - | 4.50% |  | 3.65 | % | - | 4.50% |  | N/A |  | N/A |  | N/A
Medical cost trend on covered charges: |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Initial trend rate (end of year) | N/A |  | N/A |  | N/A |  | 6.75% |  | 7.00% |  | 7.25%
Ultimate trend rate | N/A |  | N/A |  | N/A |  | 5.00% |  | 5.00% |  | 5.00%
| Qualified Defined Benefit Pension Plan |  | OPEB Plans
IPL | 2017 |  | 2016 |  | 2015 |  | 2017 |  | 2016 |  | 2015
Discount rate for benefit obligations | 3.68% |  | 4.22% |  | 4.50% |  | 3.51% |  | 3.95% |  | 4.28%
Discount rate for net periodic cost | 4.22% |  | 4.50% |  | 4.20% |  | 3.95% |  | 4.28% |  | 3.94%
Expected rate of return on plan assets | 7.60% |  | 7.60% |  | 7.60% |  | 6.20% |  | 6.60% |  | 6.60%
Rate of compensation increase | 3.65% |  | 3.65% |  | 3.65% |  | N/A |  | N/A |  | N/A
Medical cost trend on covered charges: |  |  |  |  |  |  |  |  |  |  |
Initial trend rate (end of year) | N/A |  | N/A |  | N/A |  | 6.75% |  | 7.00% |  | 7.25%
Ultimate trend rate | N/A |  | N/A |  | N/A |  | 5.00% |  | 5.00% |  | 5.00%
| Qualified Defined Benefit Pension Plan |  | OPEB Plans
WPL | 2017 |  | 2016 |  | 2015 |  | 2017 |  | 2016 |  | 2015
Discount rate for benefit obligations | 3.69% |  | 4.23% |  | 4.51% |  | 3.51% |  | 3.96% |  | 4.28%
Discount rate for net periodic cost | 4.23% |  | 4.51% |  | 4.20% |  | 3.96% |  | 4.28% |  | 3.96%
Expected rate of return on plan assets | 7.60% |  | 7.60% |  | 7.60% |  | 3.50% |  | 4.70% |  | 4.60%
Rate of compensation increase | 3.65% |  | 3.65% |  | 3.65% |  | N/A |  | N/A |  | N/A
Medical cost trend on covered charges: |  |  |  |  |  |  |  |  |  |  |
Initial trend rate (end of year) | N/A |  | N/A |  | N/A |  | 6.75% |  | 7.00% |  | 7.25%
Ultimate trend rate | N/A |  | N/A |  | N/A |  | 5.00% |  | 5.00% |  | 5.00%
Net Periodic Benefit Costs (Credits) | The components of net periodic benefit costs (credits) for sponsored defined benefit pension and OPEB plans are included in the tables below (in millions). Net periodic benefit costs are primarily included in “Other operation and maintenance” in the income statements.
Alliant Energy | Defined Benefit Pension Plans |  | OPEB Plans
2017 |  | 2016 |  | 2015 |  | 2017 |  | 2016 |  | 2015
Service cost |  | $12.5 |  |  |  | $12.6 |  |  |  | $15.9 |  |  |  | $5.0 |  |  |  | $5.3 |  |  |  | $5.5 |
Interest cost | 51.0 |  |  | 53.0 |  |  | 53.6 |  |  | 8.6 |  |  | 9.4 |  |  | 9.1 |
Expected return on plan assets (a) | (65.5 | ) |  | (65.5 | ) |  | (75.0 | ) |  | (6.1 | ) |  | (6.1 | ) |  | (8.4 | )
Amortization of prior service credit (b) | (0.4 | ) |  | (0.3 | ) |  | (0.2 | ) |  | (0.2 | ) |  | (4.1 | ) |  | (11.3 | )
Amortization of actuarial loss (c) | 37.6 |  |  | 37.4 |  |  | 35.4 |  |  | 3.8 |  |  | 4.7 |  |  | 4.8 |
Additional benefit costs | — |  |  | — |  |  | 0.5 |  |  | — |  |  | — |  |  | — |
Settlement losses (d) | 0.9 |  |  | — |  |  | — |  |  | — |  |  | — |  |  | — |
|  | $36.1 |  |  |  | $37.2 |  |  |  | $30.2 |  |  |  | $11.1 |  |  |  | $9.2 |  |  |  | ($0.3 | )
IPL | Defined Benefit Pension Plans |  | OPEB Plans
2017 |  | 2016 |  | 2015 |  | 2017 |  | 2016 |  | 2015
Service cost |  | $7.3 |  |  |  | $7.5 |  |  |  | $8.8 |  |  |  | $2.1 |  |  |  | $2.3 |  |  |  | $2.4 |
Interest cost | 23.5 |  |  | 24.5 |  |  | 25.0 |  |  | 3.5 |  |  | 3.8 |  |  | 3.8 |
Expected return on plan assets (a) | (30.8 | ) |  | (30.9 | ) |  | (35.8 | ) |  | (4.3 | ) |  | (4.3 | ) |  | (5.7 | )
Amortization of prior service credit (b) | (0.2 | ) |  | (0.2 | ) |  | (0.1 | ) |  | — |  |  | (2.6 | ) |  | (6.1 | )
Amortization of actuarial loss (c) | 16.1 |  |  | 16.5 |  |  | 15.3 |  |  | 2.0 |  |  | 2.6 |  |  | 2.3 |
|  | $15.9 |  |  |  | $17.4 |  |  |  | $13.2 |  |  |  | $3.3 |  |  |  | $1.8 |  |  |  | ($3.3 | )
WPL | Defined Benefit Pension Plans |  | OPEB Plans
2017 |  | 2016 |  | 2015 |  | 2017 |  | 2016 |  | 2015
Service cost |  | $4.9 |  |  |  | $4.9 |  |  |  | $5.8 |  |  |  | $1.9 |  |  |  | $2.0 |  |  |  | $2.1 |
Interest cost | 21.8 |  |  | 22.3 |  |  | 22.6 |  |  | 3.4 |  |  | 3.8 |  |  | 3.7 |
Expected return on plan assets (a) | (28.5 | ) |  | (28.3 | ) |  | (32.4 | ) |  | (0.8 | ) |  | (0.8 | ) |  | (1.5 | )
Amortization of prior service cost (credit) (b) | 0.1 |  |  | 0.2 |  |  | 0.2 |  |  | (0.2 | ) |  | (0.9 | ) |  | (3.5 | )
Amortization of actuarial loss (c) | 18.5 |  |  | 17.6 |  |  | 16.8 |  |  | 1.6 |  |  | 1.8 |  |  | 2.2 |
Additional benefit costs | — |  |  | — |  |  | 0.5 |  |  | — |  |  | — |  |  | — |
|  | $16.8 |  |  |  | $16.7 |  |  |  | $13.5 |  |  |  | $5.9 |  |  |  | $5.9 |  |  |  | $3.0 |
(a) | The expected return on plan assets is based on the expected rate of return on plan assets and the fair value approach to the market-related value of plan assets.
(b) | Unrecognized prior service costs (credits) for the OPEB plans are amortized over the average future service period to full eligibility of the participants of each plan.
(c) | Unrecognized net actuarial gains or losses in excess of 10% of the greater of the plans’ benefit obligations or assets are amortized over the average future service lives of plan participants, except for the Alliant Energy Cash Balance Pension Plan where gains or losses outside the 10% threshold are amortized over the time period the participants are expected to receive benefits.
(d) | Settlement losses related to payments made to retired executives of Alliant Energy.
Estimated Amortization From Regulatory Assets, Regulatory Liabilities And Accumulated Other Comprehensive Loss Into Net Periodic Benefit Cost | The estimated amortization from “Regulatory assets” and “Regulatory liabilities” on the balance sheets and AOCL on Alliant Energy’s balance sheet into net periodic benefit cost in 2018 is as follows (in millions):
| Alliant Energy |  | IPL |  | WPL
| Defined Benefit |  |  |  | Defined Benefit |  |  |  | Defined Benefit |  |
| Pension Plans |  | OPEB Plans |  | Pension Plans |  | OPEB Plans |  | Pension Plans |  | OPEB Plans
Actuarial loss |  | $35.2 |  |  |  | $3.4 |  |  |  | $15.0 |  |  |  | $1.2 |  |  |  | $17.2 |  |  |  | $2.0 |
Prior service credit | (0.7 | ) |  | (0.2 | ) |  | (0.2 | ) |  | — |  |  | (0.2 | ) |  | (0.2 | )
|  | $34.5 |  |  |  | $3.2 |  |  |  | $14.8 |  |  |  | $1.2 |  |  |  | $17.0 |  |  |  | $1.8 |
Funded Status Of Benefit Plans | A reconciliation of the funded status of qualified and non-qualified defined benefit pension and OPEB plans to the amounts recognized on the balance sheets at December 31 was as follows (in millions):
| Defined Benefit Pension Plans |  | OPEB Plans
Alliant Energy | 2017 |  | 2016 |  | 2017 |  | 2016
Change in benefit obligation: |  |  |  |  |  |  |
Net benefit obligation at January 1 |  | $1,244.3 |  |  |  | $1,206.3 |  |  |  | $220.1 |  |  |  | $221.4 |
Service cost | 12.5 |  |  | 12.6 |  |  | 5.0 |  |  | 5.3 |
Interest cost | 51.0 |  |  | 53.0 |  |  | 8.6 |  |  | 9.4 |
Plan participants’ contributions | — |  |  | — |  |  | 2.9 |  |  | 2.4 |
Actuarial (gain) loss | 83.6 |  |  | 48.3 |  |  | 5.4 |  |  | (0.3 | )
Gross benefits paid | (88.3 | ) |  | (75.9 | ) |  | (19.7 | ) |  | (18.1 | )
Net benefit obligation at December 31 | 1,303.1 |  |  | 1,244.3 |  |  | 222.3 |  |  | 220.1 |
Change in plan assets: |  |  |  |  |  |  |
Fair value of plan assets at January 1 | 895.7 |  |  | 895.0 |  |  | 105.8 |  |  | 106.9 |
Actual return on plan assets | 136.7 |  |  | 74.3 |  |  | 12.9 |  |  | 8.2 |
Employer contributions | 6.6 |  |  | 2.3 |  |  | 9.2 |  |  | 6.4 |
Plan participants’ contributions | — |  |  | — |  |  | 2.9 |  |  | 2.4 |
Gross benefits paid | (88.3 | ) |  | (75.9 | ) |  | (19.7 | ) |  | (18.1 | )
Fair value of plan assets at December 31 | 950.7 |  |  | 895.7 |  |  | 111.1 |  |  | 105.8 |
Under funded status at December 31 |  | ($352.4 | ) |  |  | ($348.6 | ) |  |  | ($111.2 | ) |  |  | ($114.3 | )
| Defined Benefit Pension Plans |  | OPEB Plans
Alliant Energy | 2017 |  | 2016 |  | 2017 |  | 2016
Amounts recognized on the balance sheets consist of: |  |  |  |  |  |  |
Non-current assets |  | $— |  |  |  | $— |  |  |  | $8.8 |  |  |  | $3.2 |
Current liabilities | (2.2 | ) |  | (6.5 | ) |  | (9.1 | ) |  | (8.6 | )
Pension and other benefit obligations | (350.2 | ) |  | (342.1 | ) |  | (110.9 | ) |  | (108.9 | )
Net amounts recognized at December 31 |  | ($352.4 | ) |  |  | ($348.6 | ) |  |  | ($111.2 | ) |  |  | ($114.3 | )
Amounts recognized in Regulatory Assets (refer to Note 2 for details) and AOCL (refer to Alliant Energy’s common equity statements for details) consist of: |  |  |  |  |  |  |
Net actuarial loss |  | $509.1 |  |  |  | $535.1 |  |  |  | $47.4 |  |  |  | $52.6 |
Prior service credit | (6.5 | ) |  | (6.9 | ) |  | (1.3 | ) |  | (1.5 | )
|  | $502.6 |  |  |  | $528.2 |  |  |  | $46.1 |  |  |  | $51.1 |
| Defined Benefit Pension Plans |  | OPEB Plans
IPL | 2017 |  | 2016 |  | 2017 |  | 2016
Change in benefit obligation: |  |  |  |  |  |  |
Net benefit obligation at January 1 |  | $570.4 |  |  |  | $556.1 |  |  |  | $90.1 |  |  |  | $91.3 |
Service cost | 7.3 |  |  | 7.5 |  |  | 2.1 |  |  | 2.3 |
Interest cost | 23.5 |  |  | 24.5 |  |  | 3.5 |  |  | 3.8 |
Plan participants’ contributions | — |  |  | — |  |  | 1.0 |  |  | 0.9 |
Actuarial (gain) loss | 34.9 |  |  | 19.1 |  |  | (0.1 | ) |  | (0.7 | )
Gross benefits paid | (43.2 | ) |  | (36.8 | ) |  | (7.2 | ) |  | (7.5 | )
Net benefit obligation at December 31 | 592.9 |  |  | 570.4 |  |  | 89.4 |  |  | 90.1 |
Change in plan assets: |  |  |  |  |  |  |
Fair value of plan assets at January 1 | 422.0 |  |  | 422.7 |  |  | 68.2 |  |  | 69.2 |
Actual return on plan assets | 64.3 |  |  | 35.3 |  |  | 8.9 |  |  | 5.3 |
Employer contributions | 0.6 |  |  | 0.8 |  |  | 2.0 |  |  | 0.3 |
Plan participants’ contributions | — |  |  | — |  |  | 1.0 |  |  | 0.9 |
Gross benefits paid | (43.2 | ) |  | (36.8 | ) |  | (7.2 | ) |  | (7.5 | )
Fair value of plan assets at December 31 | 443.7 |  |  | 422.0 |  |  | 72.9 |  |  | 68.2 |
Under funded status at December 31 |  | ($149.2 | ) |  |  | ($148.4 | ) |  |  | ($16.5 | ) |  |  | ($21.9 | )
| Defined Benefit Pension Plans |  | OPEB Plans
IPL | 2017 |  | 2016 |  | 2017 |  | 2016
Amounts recognized on the balance sheets consist of: |  |  |  |  |  |  |
Non-current assets |  | $— |  |  |  | $— |  |  |  | $5.9 |  |  |  | $0.4 |
Current liabilities | (0.5 | ) |  | (0.7 | ) |  | (2.0 | ) |  | (1.9 | )
Pension and other benefit obligations | (148.7 | ) |  | (147.7 | ) |  | (20.4 | ) |  | (20.4 | )
Net amounts recognized at December 31 |  | ($149.2 | ) |  |  | ($148.4 | ) |  |  | ($16.5 | ) |  |  | ($21.9 | )
Amounts recognized in Regulatory Assets consist of (refer to Note 2 for details): |  |  |  |  |  |  |
Net actuarial loss |  | $218.9 |  |  |  | $233.6 |  |  |  | $18.7 |  |  |  | $25.4 |
Prior service credit | (2.1 | ) |  | (2.3 | ) |  | — |  |  | — |
|  | $216.8 |  |  |  | $231.3 |  |  |  | $18.7 |  |  |  | $25.4 |
| Defined Benefit Pension Plans |  | OPEB Plans
WPL | 2017 |  | 2016 |  | 2017 |  | 2016
Change in benefit obligation: |  |  |  |  |  |  |
Net benefit obligation at January 1 |  | $529.2 |  |  |  | $505.9 |  |  |  | $88.9 |  |  |  | $89.7 |
Service cost | 4.9 |  |  | 4.9 |  |  | 1.9 |  |  | 2.0 |
Interest cost | 21.8 |  |  | 22.3 |  |  | 3.4 |  |  | 3.8 |
Plan participants’ contributions | — |  |  | — |  |  | 1.4 |  |  | 1.2 |
Actuarial loss | 38.3 |  |  | 25.7 |  |  | 4.1 |  |  | 0.5 |
Gross benefits paid | (34.4 | ) |  | (29.6 | ) |  | (9.3 | ) |  | (8.3 | )
Net benefit obligation at December 31 | 559.8 |  |  | 529.2 |  |  | 90.4 |  |  | 88.9 |
Change in plan assets: |  |  |  |  |  |  |
Fair value of plan assets at January 1 | 389.7 |  |  | 386.8 |  |  | 18.6 |  |  | 18.7 |
Actual return on plan assets | 59.6 |  |  | 32.4 |  |  | 1.2 |  |  | 1.2 |
Employer contributions | 0.1 |  |  | 0.1 |  |  | 6.8 |  |  | 5.8 |
Plan participants’ contributions | — |  |  | — |  |  | 1.4 |  |  | 1.2 |
Gross benefits paid | (34.4 | ) |  | (29.6 | ) |  | (9.3 | ) |  | (8.3 | )
Fair value of plan assets at December 31 | 415.0 |  |  | 389.7 |  |  | 18.7 |  |  | 18.6 |
Under funded status at December 31 |  | ($144.8 | ) |  |  | ($139.5 | ) |  |  | ($71.7 | ) |  |  | ($70.3 | )
| Defined Benefit Pension Plans |  | OPEB Plans
WPL | 2017 |  | 2016 |  | 2017 |  | 2016
Amounts recognized on the balance sheets consist of: |  |  |  |  |  |  |
Non-current assets |  | $— |  |  |  | $— |  |  |  | $2.9 |  |  |  | $2.7 |
Current liabilities | (0.1 | ) |  | (0.1 | ) |  | (6.8 | ) |  | (6.4 | )
Pension and other benefit obligations | (144.7 | ) |  | (139.4 | ) |  | (67.8 | ) |  | (66.6 | )
Net amounts recognized at December 31 |  | ($144.8 | ) |  |  | ($139.5 | ) |  |  | ($71.7 | ) |  |  | ($70.3 | )
Amounts recognized in Regulatory Assets consist of (refer to Note 2 for details): |  |  |  |  |  |  |
Net actuarial loss |  | $224.7 |  |  |  | $236.1 |  |  |  | $23.6 |  |  |  | $21.5 |
Prior service credit | (1.5 | ) |  | (1.4 | ) |  | (1.3 | ) |  | (1.5 | )
|  | $223.2 |  |  |  | $234.7 |  |  |  | $22.3 |  |  |  | $20.0 |
Accumulated Benefit Obligations | Included in the following tables are accumulated benefit obligations, aggregate amounts applicable to defined benefit pension and OPEB plans with accumulated benefit obligations in excess of plan assets, as well as defined benefit pension plans with projected benefit obligations in excess of plan assets as of the December 31 measurement date (in millions):
| Defined Benefit Pension Plans |  | OPEB Plans
Alliant Energy | 2017 |  | 2016 |  | 2017 |  | 2016
Accumulated benefit obligations |  | $1,269.0 |  |  |  | $1,201.5 |  |  |  | $222.3 |  |  |  | $220.1 |
Plans with accumulated benefit obligations in excess of plan assets: |  |  |  |  |  |  |
Accumulated benefit obligations | 1,269.0 |  |  | 1,201.5 |  |  | 222.3 |  |  | 220.1 |
Fair value of plan assets | 950.7 |  |  | 895.7 |  |  | 111.1 |  |  | 105.8 |
Plans with projected benefit obligations in excess of plan assets: |  |  |  |  |  |  |
Projected benefit obligations | 1,303.1 |  |  | 1,244.3 |  |  | N/A |  |  | N/A |
Fair value of plan assets | 950.7 |  |  | 895.7 |  |  | N/A |  |  | N/A |
| Defined Benefit Pension Plans |  | OPEB Plans
IPL | 2017 |  | 2016 |  | 2017 |  | 2016
Accumulated benefit obligations |  | $573.1 |  |  |  | $546.7 |  |  |  | $89.4 |  |  |  | $90.1 |
Plans with accumulated benefit obligations in excess of plan assets: |  |  |  |  |  |  |
Accumulated benefit obligations | 573.1 |  |  | 546.7 |  |  | 89.4 |  |  | 90.1 |
Fair value of plan assets | 443.7 |  |  | 422.0 |  |  | 72.9 |  |  | 68.2 |
Plans with projected benefit obligations in excess of plan assets: |  |  |  |  |  |  |
Projected benefit obligations | 592.9 |  |  | 570.4 |  |  | N/A |  |  | N/A |
Fair value of plan assets | 443.7 |  |  | 422.0 |  |  | N/A |  |  | N/A |
| Defined Benefit Pension Plans |  | OPEB Plans
WPL | 2017 |  | 2016 |  | 2017 |  | 2016
Accumulated benefit obligations |  | $548.1 |  |  |  | $513.2 |  |  |  | $90.4 |  |  |  | $88.9 |
Plans with accumulated benefit obligations in excess of plan assets: |  |  |  |  |  |  |
Accumulated benefit obligations | 548.1 |  |  | 513.2 |  |  | 90.4 |  |  | 88.9 |
Fair value of plan assets | 415.0 |  |  | 389.7 |  |  | 18.7 |  |  | 18.6 |
Plans with projected benefit obligations in excess of plan assets: |  |  |  |  |  |  |
Projected benefit obligations | 559.8 |  |  | 529.2 |  |  | N/A |  |  | N/A |
Fair value of plan assets | 415.0 |  |  | 389.7 |  |  | N/A |  |  | N/A |
Regulatory Assets | In addition to the amounts recognized in regulatory assets in the above tables for IPL and WPL, regulatory assets were recognized for amounts associated with Corporate Services employees participating in other Alliant Energy sponsored benefit plans that were allocated to IPL and WPL at December 31 as follows (in millions):
| IPL |  | WPL
| 2017 |  | 2016 |  | 2017 |  | 2016
Regulatory assets |  | $38.9 |  |  |  | $37.3 |  |  |  | $28.1 |  |  |  | $30.0 |
Estimated Future Employer Contributions | Estimated funding for the qualified and non-qualified defined benefit pension and OPEB plans for 2018 is as follows (in millions):
| Alliant Energy |  | IPL |  | WPL
Defined benefit pension plans (a) |  | $6.3 |  |  |  | $4.4 |  |  |  | $0.3 |
OPEB plans | 9.0 |  |  | 2.0 |  |  | 6.8 |
(a) | Alliant Energy sponsors several non-qualified defined benefit pension plans that cover certain current and former key employees of IPL and WPL. Alliant Energy allocates pension costs to IPL and WPL for these plans. In addition, IPL and WPL amounts reflect funding for their non-bargaining employees who are participants in the Alliant Energy and Corporate Services sponsored qualified and non-qualified defined benefit pension plans.
Expected Benefit Payments | Expected benefit payments for the qualified and non-qualified defined benefit plans, which reflect expected future service, as appropriate, are as follows (in millions):
Alliant Energy | 2018 |  | 2019 |  | 2020 |  | 2021 |  | 2022 |  | 2023 - 2027
Defined benefit pension benefits |  | $72.2 |  |  |  | $73.9 |  |  |  | $76.4 |  |  |  | $77.1 |  |  |  | $92.9 |  |  |  | $398.2 |
OPEB | 18.2 |  |  | 18.4 |  |  | 17.7 |  |  | 17.5 |  |  | 17.2 |  |  | 80.1 |
|  | $90.4 |  |  |  | $92.3 |  |  |  | $94.1 |  |  |  | $94.6 |  |  |  | $110.1 |  |  |  | $478.3 |
IPL | 2018 |  | 2019 |  | 2020 |  | 2021 |  | 2022 |  | 2023 - 2027
Defined benefit pension benefits |  | $33.9 |  |  |  | $33.8 |  |  |  | $36.5 |  |  |  | $36.6 |  |  |  | $37.6 |  |  |  | $188.4 |
OPEB | 7.1 |  |  | 7.1 |  |  | 7.2 |  |  | 7.1 |  |  | 7.0 |  |  | 32.6 |
|  | $41.0 |  |  |  | $40.9 |  |  |  | $43.7 |  |  |  | $43.7 |  |  |  | $44.6 |  |  |  | $221.0 |
WPL | 2018 |  | 2019 |  | 2020 |  | 2021 |  | 2022 |  | 2023 - 2027
Defined benefit pension benefits |  | $31.4 |  |  |  | $32.0 |  |  |  | $32.4 |  |  |  | $32.4 |  |  |  | $32.7 |  |  |  | $167.8 |
OPEB | 8.3 |  |  | 8.3 |  |  | 7.5 |  |  | 7.3 |  |  | 7.0 |  |  | 31.8 |
|  | $39.7 |  |  |  | $40.3 |  |  |  | $39.9 |  |  |  | $39.7 |  |  |  | $39.7 |  |  |  | $199.6 |
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 was as follows (in millions):
| Alliant Energy |  | IPL |  | WPL
| 2017 |  | 2016 |  | 2015 |  | 2017 |  | 2016 |  | 2015 |  | 2017 |  | 2016 |  | 2015
Compensation expense |  | $15.1 |  |  |  | $18.0 |  |  |  | $10.7 |  |  |  | $8.3 |  |  |  | $9.5 |  |  |  | $5.7 |  |  |  | $6.4 |  |  |  | $7.9 |  |  |  | $4.7 |
Income tax benefits | 6.2 |  |  | 7.4 |  |  | 4.4 |  |  | 3.4 |  |  | 4.0 |  |  | 2.4 |  |  | 2.6 |  |  | 3.2 |  |  | 1.9 |
Schedule of Carrying Value and Fair Market Value of the Deferred Compensation Obligation | At December 31, the carrying value of the deferred compensation obligation for the company stock account and the shares in the deferred compensation trust based on the historical value of the shares of Alliant Energy common stock contributed to the rabbi trust, and the fair market value of the shares held in the rabbi trust, were as follows (in millions):
| 2017 |  | 2016
Carrying value |  | $11.1 |  |  |  | $10.0 |
Fair market value | 19.7 |  |  | 16.7 |
IPL [Member] |
Defined Benefit Plan Disclosure [Line Items] |
Assumptions Used To Measure Benefit Plans | The assumptions for defined benefit pension and OPEB plans at the measurement date of December 31 were as follows:
| Defined Benefit Pension Plans |  | OPEB Plans
Alliant Energy | 2017 |  | 2016 |  | 2015 |  | 2017 |  | 2016 |  | 2015
Discount rate for benefit obligations | 3.66% |  | 4.19% |  | 4.47% |  | 3.53% |  | 3.98% |  | 4.30%
Discount rate for net periodic cost | 4.19% |  | 4.47% |  | 4.18% |  | 3.98% |  | 4.30% |  | 3.97%
Expected rate of return on plan assets | 7.60% |  | 7.60% |  | 7.60% |  | 5.80% |  | 6.30% |  | 6.20%
Rate of compensation increase | 3.65 | % | - | 4.50% |  | 3.65 | % | - | 4.50% |  | 3.65 | % | - | 4.50% |  | N/A |  | N/A |  | N/A
Medical cost trend on covered charges: |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Initial trend rate (end of year) | N/A |  | N/A |  | N/A |  | 6.75% |  | 7.00% |  | 7.25%
Ultimate trend rate | N/A |  | N/A |  | N/A |  | 5.00% |  | 5.00% |  | 5.00%
| Qualified Defined Benefit Pension Plan |  | OPEB Plans
IPL | 2017 |  | 2016 |  | 2015 |  | 2017 |  | 2016 |  | 2015
Discount rate for benefit obligations | 3.68% |  | 4.22% |  | 4.50% |  | 3.51% |  | 3.95% |  | 4.28%
Discount rate for net periodic cost | 4.22% |  | 4.50% |  | 4.20% |  | 3.95% |  | 4.28% |  | 3.94%
Expected rate of return on plan assets | 7.60% |  | 7.60% |  | 7.60% |  | 6.20% |  | 6.60% |  | 6.60%
Rate of compensation increase | 3.65% |  | 3.65% |  | 3.65% |  | N/A |  | N/A |  | N/A
Medical cost trend on covered charges: |  |  |  |  |  |  |  |  |  |  |
Initial trend rate (end of year) | N/A |  | N/A |  | N/A |  | 6.75% |  | 7.00% |  | 7.25%
Ultimate trend rate | N/A |  | N/A |  | N/A |  | 5.00% |  | 5.00% |  | 5.00%
| Qualified Defined Benefit Pension Plan |  | OPEB Plans
WPL | 2017 |  | 2016 |  | 2015 |  | 2017 |  | 2016 |  | 2015
Discount rate for benefit obligations | 3.69% |  | 4.23% |  | 4.51% |  | 3.51% |  | 3.96% |  | 4.28%
Discount rate for net periodic cost | 4.23% |  | 4.51% |  | 4.20% |  | 3.96% |  | 4.28% |  | 3.96%
Expected rate of return on plan assets | 7.60% |  | 7.60% |  | 7.60% |  | 3.50% |  | 4.70% |  | 4.60%
Rate of compensation increase | 3.65% |  | 3.65% |  | 3.65% |  | N/A |  | N/A |  | N/A
Medical cost trend on covered charges: |  |  |  |  |  |  |  |  |  |  |
Initial trend rate (end of year) | N/A |  | N/A |  | N/A |  | 6.75% |  | 7.00% |  | 7.25%
Ultimate trend rate | N/A |  | N/A |  | N/A |  | 5.00% |  | 5.00% |  | 5.00%
Net Periodic Benefit Costs (Credits) | The components of net periodic benefit costs (credits) for sponsored defined benefit pension and OPEB plans are included in the tables below (in millions). Net periodic benefit costs are primarily included in “Other operation and maintenance” in the income statements.
Alliant Energy | Defined Benefit Pension Plans |  | OPEB Plans
2017 |  | 2016 |  | 2015 |  | 2017 |  | 2016 |  | 2015
Service cost |  | $12.5 |  |  |  | $12.6 |  |  |  | $15.9 |  |  |  | $5.0 |  |  |  | $5.3 |  |  |  | $5.5 |
Interest cost | 51.0 |  |  | 53.0 |  |  | 53.6 |  |  | 8.6 |  |  | 9.4 |  |  | 9.1 |
Expected return on plan assets (a) | (65.5 | ) |  | (65.5 | ) |  | (75.0 | ) |  | (6.1 | ) |  | (6.1 | ) |  | (8.4 | )
Amortization of prior service credit (b) | (0.4 | ) |  | (0.3 | ) |  | (0.2 | ) |  | (0.2 | ) |  | (4.1 | ) |  | (11.3 | )
Amortization of actuarial loss (c) | 37.6 |  |  | 37.4 |  |  | 35.4 |  |  | 3.8 |  |  | 4.7 |  |  | 4.8 |
Additional benefit costs | — |  |  | — |  |  | 0.5 |  |  | — |  |  | — |  |  | — |
Settlement losses (d) | 0.9 |  |  | — |  |  | — |  |  | — |  |  | — |  |  | — |
|  | $36.1 |  |  |  | $37.2 |  |  |  | $30.2 |  |  |  | $11.1 |  |  |  | $9.2 |  |  |  | ($0.3 | )
IPL | Defined Benefit Pension Plans |  | OPEB Plans
2017 |  | 2016 |  | 2015 |  | 2017 |  | 2016 |  | 2015
Service cost |  | $7.3 |  |  |  | $7.5 |  |  |  | $8.8 |  |  |  | $2.1 |  |  |  | $2.3 |  |  |  | $2.4 |
Interest cost | 23.5 |  |  | 24.5 |  |  | 25.0 |  |  | 3.5 |  |  | 3.8 |  |  | 3.8 |
Expected return on plan assets (a) | (30.8 | ) |  | (30.9 | ) |  | (35.8 | ) |  | (4.3 | ) |  | (4.3 | ) |  | (5.7 | )
Amortization of prior service credit (b) | (0.2 | ) |  | (0.2 | ) |  | (0.1 | ) |  | — |  |  | (2.6 | ) |  | (6.1 | )
Amortization of actuarial loss (c) | 16.1 |  |  | 16.5 |  |  | 15.3 |  |  | 2.0 |  |  | 2.6 |  |  | 2.3 |
|  | $15.9 |  |  |  | $17.4 |  |  |  | $13.2 |  |  |  | $3.3 |  |  |  | $1.8 |  |  |  | ($3.3 | )
WPL | Defined Benefit Pension Plans |  | OPEB Plans
2017 |  | 2016 |  | 2015 |  | 2017 |  | 2016 |  | 2015
Service cost |  | $4.9 |  |  |  | $4.9 |  |  |  | $5.8 |  |  |  | $1.9 |  |  |  | $2.0 |  |  |  | $2.1 |
Interest cost | 21.8 |  |  | 22.3 |  |  | 22.6 |  |  | 3.4 |  |  | 3.8 |  |  | 3.7 |
Expected return on plan assets (a) | (28.5 | ) |  | (28.3 | ) |  | (32.4 | ) |  | (0.8 | ) |  | (0.8 | ) |  | (1.5 | )
Amortization of prior service cost (credit) (b) | 0.1 |  |  | 0.2 |  |  | 0.2 |  |  | (0.2 | ) |  | (0.9 | ) |  | (3.5 | )
Amortization of actuarial loss (c) | 18.5 |  |  | 17.6 |  |  | 16.8 |  |  | 1.6 |  |  | 1.8 |  |  | 2.2 |
Additional benefit costs | — |  |  | — |  |  | 0.5 |  |  | — |  |  | — |  |  | — |
|  | $16.8 |  |  |  | $16.7 |  |  |  | $13.5 |  |  |  | $5.9 |  |  |  | $5.9 |  |  |  | $3.0 |
(a) | The expected return on plan assets is based on the expected rate of return on plan assets and the fair value approach to the market-related value of plan assets.
(b) | Unrecognized prior service costs (credits) for the OPEB plans are amortized over the average future service period to full eligibility of the participants of each plan.
(c) | Unrecognized net actuarial gains or losses in excess of 10% of the greater of the plans’ benefit obligations or assets are amortized over the average future service lives of plan participants, except for the Alliant Energy Cash Balance Pension Plan where gains or losses outside the 10% threshold are amortized over the time period the participants are expected to receive benefits.
(d) | Settlement losses related to payments made to retired executives of Alliant Energy.
Estimated Amortization From Regulatory Assets, Regulatory Liabilities And Accumulated Other Comprehensive Loss Into Net Periodic Benefit Cost | The estimated amortization from “Regulatory assets” and “Regulatory liabilities” on the balance sheets and AOCL on Alliant Energy’s balance sheet into net periodic benefit cost in 2018 is as follows (in millions):
| Alliant Energy |  | IPL |  | WPL
| Defined Benefit |  |  |  | Defined Benefit |  |  |  | Defined Benefit |  |
| Pension Plans |  | OPEB Plans |  | Pension Plans |  | OPEB Plans |  | Pension Plans |  | OPEB Plans
Actuarial loss |  | $35.2 |  |  |  | $3.4 |  |  |  | $15.0 |  |  |  | $1.2 |  |  |  | $17.2 |  |  |  | $2.0 |
Prior service credit | (0.7 | ) |  | (0.2 | ) |  | (0.2 | ) |  | — |  |  | (0.2 | ) |  | (0.2 | )
|  | $34.5 |  |  |  | $3.2 |  |  |  | $14.8 |  |  |  | $1.2 |  |  |  | $17.0 |  |  |  | $1.8 |
Funded Status Of Benefit Plans | A reconciliation of the funded status of qualified and non-qualified defined benefit pension and OPEB plans to the amounts recognized on the balance sheets at December 31 was as follows (in millions):
| Defined Benefit Pension Plans |  | OPEB Plans
Alliant Energy | 2017 |  | 2016 |  | 2017 |  | 2016
Change in benefit obligation: |  |  |  |  |  |  |
Net benefit obligation at January 1 |  | $1,244.3 |  |  |  | $1,206.3 |  |  |  | $220.1 |  |  |  | $221.4 |
Service cost | 12.5 |  |  | 12.6 |  |  | 5.0 |  |  | 5.3 |
Interest cost | 51.0 |  |  | 53.0 |  |  | 8.6 |  |  | 9.4 |
Plan participants’ contributions | — |  |  | — |  |  | 2.9 |  |  | 2.4 |
Actuarial (gain) loss | 83.6 |  |  | 48.3 |  |  | 5.4 |  |  | (0.3 | )
Gross benefits paid | (88.3 | ) |  | (75.9 | ) |  | (19.7 | ) |  | (18.1 | )
Net benefit obligation at December 31 | 1,303.1 |  |  | 1,244.3 |  |  | 222.3 |  |  | 220.1 |
Change in plan assets: |  |  |  |  |  |  |
Fair value of plan assets at January 1 | 895.7 |  |  | 895.0 |  |  | 105.8 |  |  | 106.9 |
Actual return on plan assets | 136.7 |  |  | 74.3 |  |  | 12.9 |  |  | 8.2 |
Employer contributions | 6.6 |  |  | 2.3 |  |  | 9.2 |  |  | 6.4 |
Plan participants’ contributions | — |  |  | — |  |  | 2.9 |  |  | 2.4 |
Gross benefits paid | (88.3 | ) |  | (75.9 | ) |  | (19.7 | ) |  | (18.1 | )
Fair value of plan assets at December 31 | 950.7 |  |  | 895.7 |  |  | 111.1 |  |  | 105.8 |
Under funded status at December 31 |  | ($352.4 | ) |  |  | ($348.6 | ) |  |  | ($111.2 | ) |  |  | ($114.3 | )
| Defined Benefit Pension Plans |  | OPEB Plans
Alliant Energy | 2017 |  | 2016 |  | 2017 |  | 2016
Amounts recognized on the balance sheets consist of: |  |  |  |  |  |  |
Non-current assets |  | $— |  |  |  | $— |  |  |  | $8.8 |  |  |  | $3.2 |
Current liabilities | (2.2 | ) |  | (6.5 | ) |  | (9.1 | ) |  | (8.6 | )
Pension and other benefit obligations | (350.2 | ) |  | (342.1 | ) |  | (110.9 | ) |  | (108.9 | )
Net amounts recognized at December 31 |  | ($352.4 | ) |  |  | ($348.6 | ) |  |  | ($111.2 | ) |  |  | ($114.3 | )
Amounts recognized in Regulatory Assets (refer to Note 2 for details) and AOCL (refer to Alliant Energy’s common equity statements for details) consist of: |  |  |  |  |  |  |
Net actuarial loss |  | $509.1 |  |  |  | $535.1 |  |  |  | $47.4 |  |  |  | $52.6 |
Prior service credit | (6.5 | ) |  | (6.9 | ) |  | (1.3 | ) |  | (1.5 | )
|  | $502.6 |  |  |  | $528.2 |  |  |  | $46.1 |  |  |  | $51.1 |
| Defined Benefit Pension Plans |  | OPEB Plans
IPL | 2017 |  | 2016 |  | 2017 |  | 2016
Change in benefit obligation: |  |  |  |  |  |  |
Net benefit obligation at January 1 |  | $570.4 |  |  |  | $556.1 |  |  |  | $90.1 |  |  |  | $91.3 |
Service cost | 7.3 |  |  | 7.5 |  |  | 2.1 |  |  | 2.3 |
Interest cost | 23.5 |  |  | 24.5 |  |  | 3.5 |  |  | 3.8 |
Plan participants’ contributions | — |  |  | — |  |  | 1.0 |  |  | 0.9 |
Actuarial (gain) loss | 34.9 |  |  | 19.1 |  |  | (0.1 | ) |  | (0.7 | )
Gross benefits paid | (43.2 | ) |  | (36.8 | ) |  | (7.2 | ) |  | (7.5 | )
Net benefit obligation at December 31 | 592.9 |  |  | 570.4 |  |  | 89.4 |  |  | 90.1 |
Change in plan assets: |  |  |  |  |  |  |
Fair value of plan assets at January 1 | 422.0 |  |  | 422.7 |  |  | 68.2 |  |  | 69.2 |
Actual return on plan assets | 64.3 |  |  | 35.3 |  |  | 8.9 |  |  | 5.3 |
Employer contributions | 0.6 |  |  | 0.8 |  |  | 2.0 |  |  | 0.3 |
Plan participants’ contributions | — |  |  | — |  |  | 1.0 |  |  | 0.9 |
Gross benefits paid | (43.2 | ) |  | (36.8 | ) |  | (7.2 | ) |  | (7.5 | )
Fair value of plan assets at December 31 | 443.7 |  |  | 422.0 |  |  | 72.9 |  |  | 68.2 |
Under funded status at December 31 |  | ($149.2 | ) |  |  | ($148.4 | ) |  |  | ($16.5 | ) |  |  | ($21.9 | )
| Defined Benefit Pension Plans |  | OPEB Plans
IPL | 2017 |  | 2016 |  | 2017 |  | 2016
Amounts recognized on the balance sheets consist of: |  |  |  |  |  |  |
Non-current assets |  | $— |  |  |  | $— |  |  |  | $5.9 |  |  |  | $0.4 |
Current liabilities | (0.5 | ) |  | (0.7 | ) |  | (2.0 | ) |  | (1.9 | )
Pension and other benefit obligations | (148.7 | ) |  | (147.7 | ) |  | (20.4 | ) |  | (20.4 | )
Net amounts recognized at December 31 |  | ($149.2 | ) |  |  | ($148.4 | ) |  |  | ($16.5 | ) |  |  | ($21.9 | )
Amounts recognized in Regulatory Assets consist of (refer to Note 2 for details): |  |  |  |  |  |  |
Net actuarial loss |  | $218.9 |  |  |  | $233.6 |  |  |  | $18.7 |  |  |  | $25.4 |
Prior service credit | (2.1 | ) |  | (2.3 | ) |  | — |  |  | — |
|  | $216.8 |  |  |  | $231.3 |  |  |  | $18.7 |  |  |  | $25.4 |
| Defined Benefit Pension Plans |  | OPEB Plans
WPL | 2017 |  | 2016 |  | 2017 |  | 2016
Change in benefit obligation: |  |  |  |  |  |  |
Net benefit obligation at January 1 |  | $529.2 |  |  |  | $505.9 |  |  |  | $88.9 |  |  |  | $89.7 |
Service cost | 4.9 |  |  | 4.9 |  |  | 1.9 |  |  | 2.0 |
Interest cost | 21.8 |  |  | 22.3 |  |  | 3.4 |  |  | 3.8 |
Plan participants’ contributions | — |  |  | — |  |  | 1.4 |  |  | 1.2 |
Actuarial loss | 38.3 |  |  | 25.7 |  |  | 4.1 |  |  | 0.5 |
Gross benefits paid | (34.4 | ) |  | (29.6 | ) |  | (9.3 | ) |  | (8.3 | )
Net benefit obligation at December 31 | 559.8 |  |  | 529.2 |  |  | 90.4 |  |  | 88.9 |
Change in plan assets: |  |  |  |  |  |  |
Fair value of plan assets at January 1 | 389.7 |  |  | 386.8 |  |  | 18.6 |  |  | 18.7 |
Actual return on plan assets | 59.6 |  |  | 32.4 |  |  | 1.2 |  |  | 1.2 |
Employer contributions | 0.1 |  |  | 0.1 |  |  | 6.8 |  |  | 5.8 |
Plan participants’ contributions | — |  |  | — |  |  | 1.4 |  |  | 1.2 |
Gross benefits paid | (34.4 | ) |  | (29.6 | ) |  | (9.3 | ) |  | (8.3 | )
Fair value of plan assets at December 31 | 415.0 |  |  | 389.7 |  |  | 18.7 |  |  | 18.6 |
Under funded status at December 31 |  | ($144.8 | ) |  |  | ($139.5 | ) |  |  | ($71.7 | ) |  |  | ($70.3 | )
| Defined Benefit Pension Plans |  | OPEB Plans
WPL | 2017 |  | 2016 |  | 2017 |  | 2016
Amounts recognized on the balance sheets consist of: |  |  |  |  |  |  |
Non-current assets |  | $— |  |  |  | $— |  |  |  | $2.9 |  |  |  | $2.7 |
Current liabilities | (0.1 | ) |  | (0.1 | ) |  | (6.8 | ) |  | (6.4 | )
Pension and other benefit obligations | (144.7 | ) |  | (139.4 | ) |  | (67.8 | ) |  | (66.6 | )
Net amounts recognized at December 31 |  | ($144.8 | ) |  |  | ($139.5 | ) |  |  | ($71.7 | ) |  |  | ($70.3 | )
Amounts recognized in Regulatory Assets consist of (refer to Note 2 for details): |  |  |  |  |  |  |
Net actuarial loss |  | $224.7 |  |  |  | $236.1 |  |  |  | $23.6 |  |  |  | $21.5 |
Prior service credit | (1.5 | ) |  | (1.4 | ) |  | (1.3 | ) |  | (1.5 | )
|  | $223.2 |  |  |  | $234.7 |  |  |  | $22.3 |  |  |  | $20.0 |
Accumulated Benefit Obligations | Included in the following tables are accumulated benefit obligations, aggregate amounts applicable to defined benefit pension and OPEB plans with accumulated benefit obligations in excess of plan assets, as well as defined benefit pension plans with projected benefit obligations in excess of plan assets as of the December 31 measurement date (in millions):
| Defined Benefit Pension Plans |  | OPEB Plans
Alliant Energy | 2017 |  | 2016 |  | 2017 |  | 2016
Accumulated benefit obligations |  | $1,269.0 |  |  |  | $1,201.5 |  |  |  | $222.3 |  |  |  | $220.1 |
Plans with accumulated benefit obligations in excess of plan assets: |  |  |  |  |  |  |
Accumulated benefit obligations | 1,269.0 |  |  | 1,201.5 |  |  | 222.3 |  |  | 220.1 |
Fair value of plan assets | 950.7 |  |  | 895.7 |  |  | 111.1 |  |  | 105.8 |
Plans with projected benefit obligations in excess of plan assets: |  |  |  |  |  |  |
Projected benefit obligations | 1,303.1 |  |  | 1,244.3 |  |  | N/A |  |  | N/A |
Fair value of plan assets | 950.7 |  |  | 895.7 |  |  | N/A |  |  | N/A |
| Defined Benefit Pension Plans |  | OPEB Plans
IPL | 2017 |  | 2016 |  | 2017 |  | 2016
Accumulated benefit obligations |  | $573.1 |  |  |  | $546.7 |  |  |  | $89.4 |  |  |  | $90.1 |
Plans with accumulated benefit obligations in excess of plan assets: |  |  |  |  |  |  |
Accumulated benefit obligations | 573.1 |  |  | 546.7 |  |  | 89.4 |  |  | 90.1 |
Fair value of plan assets | 443.7 |  |  | 422.0 |  |  | 72.9 |  |  | 68.2 |
Plans with projected benefit obligations in excess of plan assets: |  |  |  |  |  |  |
Projected benefit obligations | 592.9 |  |  | 570.4 |  |  | N/A |  |  | N/A |
Fair value of plan assets | 443.7 |  |  | 422.0 |  |  | N/A |  |  | N/A |
| Defined Benefit Pension Plans |  | OPEB Plans
WPL | 2017 |  | 2016 |  | 2017 |  | 2016
Accumulated benefit obligations |  | $548.1 |  |  |  | $513.2 |  |  |  | $90.4 |  |  |  | $88.9 |
Plans with accumulated benefit obligations in excess of plan assets: |  |  |  |  |  |  |
Accumulated benefit obligations | 548.1 |  |  | 513.2 |  |  | 90.4 |  |  | 88.9 |
Fair value of plan assets | 415.0 |  |  | 389.7 |  |  | 18.7 |  |  | 18.6 |
Plans with projected benefit obligations in excess of plan assets: |  |  |  |  |  |  |
Projected benefit obligations | 559.8 |  |  | 529.2 |  |  | N/A |  |  | N/A |
Fair value of plan assets | 415.0 |  |  | 389.7 |  |  | N/A |  |  | N/A |
Regulatory Assets | In addition to the amounts recognized in regulatory assets in the above tables for IPL and WPL, regulatory assets were recognized for amounts associated with Corporate Services employees participating in other Alliant Energy sponsored benefit plans that were allocated to IPL and WPL at December 31 as follows (in millions):
| IPL |  | WPL
| 2017 |  | 2016 |  | 2017 |  | 2016
Regulatory assets |  | $38.9 |  |  |  | $37.3 |  |  |  | $28.1 |  |  |  | $30.0 |
Estimated Future Employer Contributions | Estimated funding for the qualified and non-qualified defined benefit pension and OPEB plans for 2018 is as follows (in millions):
| Alliant Energy |  | IPL |  | WPL
Defined benefit pension plans (a) |  | $6.3 |  |  |  | $4.4 |  |  |  | $0.3 |
OPEB plans | 9.0 |  |  | 2.0 |  |  | 6.8 |
(a) | Alliant Energy sponsors several non-qualified defined benefit pension plans that cover certain current and former key employees of IPL and WPL. Alliant Energy allocates pension costs to IPL and WPL for these plans. In addition, IPL and WPL amounts reflect funding for their non-bargaining employees who are participants in the Alliant Energy and Corporate Services sponsored qualified and non-qualified defined benefit pension plans.
Expected Benefit Payments | Expected benefit payments for the qualified and non-qualified defined benefit plans, which reflect expected future service, as appropriate, are as follows (in millions):
Alliant Energy | 2018 |  | 2019 |  | 2020 |  | 2021 |  | 2022 |  | 2023 - 2027
Defined benefit pension benefits |  | $72.2 |  |  |  | $73.9 |  |  |  | $76.4 |  |  |  | $77.1 |  |  |  | $92.9 |  |  |  | $398.2 |
OPEB | 18.2 |  |  | 18.4 |  |  | 17.7 |  |  | 17.5 |  |  | 17.2 |  |  | 80.1 |
|  | $90.4 |  |  |  | $92.3 |  |  |  | $94.1 |  |  |  | $94.6 |  |  |  | $110.1 |  |  |  | $478.3 |
IPL | 2018 |  | 2019 |  | 2020 |  | 2021 |  | 2022 |  | 2023 - 2027
Defined benefit pension benefits |  | $33.9 |  |  |  | $33.8 |  |  |  | $36.5 |  |  |  | $36.6 |  |  |  | $37.6 |  |  |  | $188.4 |
OPEB | 7.1 |  |  | 7.1 |  |  | 7.2 |  |  | 7.1 |  |  | 7.0 |  |  | 32.6 |
|  | $41.0 |  |  |  | $40.9 |  |  |  | $43.7 |  |  |  | $43.7 |  |  |  | $44.6 |  |  |  | $221.0 |
WPL | 2018 |  | 2019 |  | 2020 |  | 2021 |  | 2022 |  | 2023 - 2027
Defined benefit pension benefits |  | $31.4 |  |  |  | $32.0 |  |  |  | $32.4 |  |  |  | $32.4 |  |  |  | $32.7 |  |  |  | $167.8 |
OPEB | 8.3 |  |  | 8.3 |  |  | 7.5 |  |  | 7.3 |  |  | 7.0 |  |  | 31.8 |
|  | $39.7 |  |  |  | $40.3 |  |  |  | $39.9 |  |  |  | $39.7 |  |  |  | $39.7 |  |  |  | $199.6 |
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 was as follows (in millions):
| Alliant Energy |  | IPL |  | WPL
| 2017 |  | 2016 |  | 2015 |  | 2017 |  | 2016 |  | 2015 |  | 2017 |  | 2016 |  | 2015
Compensation expense |  | $15.1 |  |  |  | $18.0 |  |  |  | $10.7 |  |  |  | $8.3 |  |  |  | $9.5 |  |  |  | $5.7 |  |  |  | $6.4 |  |  |  | $7.9 |  |  |  | $4.7 |
Income tax benefits | 6.2 |  |  | 7.4 |  |  | 4.4 |  |  | 3.4 |  |  | 4.0 |  |  | 2.4 |  |  | 2.6 |  |  | 3.2 |  |  | 1.9 |
WPL [Member] |
Defined Benefit Plan Disclosure [Line Items] |
Assumptions Used To Measure Benefit Plans | The assumptions for defined benefit pension and OPEB plans at the measurement date of December 31 were as follows:
| Defined Benefit Pension Plans |  | OPEB Plans
Alliant Energy | 2017 |  | 2016 |  | 2015 |  | 2017 |  | 2016 |  | 2015
Discount rate for benefit obligations | 3.66% |  | 4.19% |  | 4.47% |  | 3.53% |  | 3.98% |  | 4.30%
Discount rate for net periodic cost | 4.19% |  | 4.47% |  | 4.18% |  | 3.98% |  | 4.30% |  | 3.97%
Expected rate of return on plan assets | 7.60% |  | 7.60% |  | 7.60% |  | 5.80% |  | 6.30% |  | 6.20%
Rate of compensation increase | 3.65 | % | - | 4.50% |  | 3.65 | % | - | 4.50% |  | 3.65 | % | - | 4.50% |  | N/A |  | N/A |  | N/A
Medical cost trend on covered charges: |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Initial trend rate (end of year) | N/A |  | N/A |  | N/A |  | 6.75% |  | 7.00% |  | 7.25%
Ultimate trend rate | N/A |  | N/A |  | N/A |  | 5.00% |  | 5.00% |  | 5.00%
| Qualified Defined Benefit Pension Plan |  | OPEB Plans
IPL | 2017 |  | 2016 |  | 2015 |  | 2017 |  | 2016 |  | 2015
Discount rate for benefit obligations | 3.68% |  | 4.22% |  | 4.50% |  | 3.51% |  | 3.95% |  | 4.28%
Discount rate for net periodic cost | 4.22% |  | 4.50% |  | 4.20% |  | 3.95% |  | 4.28% |  | 3.94%
Expected rate of return on plan assets | 7.60% |  | 7.60% |  | 7.60% |  | 6.20% |  | 6.60% |  | 6.60%
Rate of compensation increase | 3.65% |  | 3.65% |  | 3.65% |  | N/A |  | N/A |  | N/A
Medical cost trend on covered charges: |  |  |  |  |  |  |  |  |  |  |
Initial trend rate (end of year) | N/A |  | N/A |  | N/A |  | 6.75% |  | 7.00% |  | 7.25%
Ultimate trend rate | N/A |  | N/A |  | N/A |  | 5.00% |  | 5.00% |  | 5.00%
| Qualified Defined Benefit Pension Plan |  | OPEB Plans
WPL | 2017 |  | 2016 |  | 2015 |  | 2017 |  | 2016 |  | 2015
Discount rate for benefit obligations | 3.69% |  | 4.23% |  | 4.51% |  | 3.51% |  | 3.96% |  | 4.28%
Discount rate for net periodic cost | 4.23% |  | 4.51% |  | 4.20% |  | 3.96% |  | 4.28% |  | 3.96%
Expected rate of return on plan assets | 7.60% |  | 7.60% |  | 7.60% |  | 3.50% |  | 4.70% |  | 4.60%
Rate of compensation increase | 3.65% |  | 3.65% |  | 3.65% |  | N/A |  | N/A |  | N/A
Medical cost trend on covered charges: |  |  |  |  |  |  |  |  |  |  |
Initial trend rate (end of year) | N/A |  | N/A |  | N/A |  | 6.75% |  | 7.00% |  | 7.25%
Ultimate trend rate | N/A |  | N/A |  | N/A |  | 5.00% |  | 5.00% |  | 5.00%
Net Periodic Benefit Costs (Credits) | The components of net periodic benefit costs (credits) for sponsored defined benefit pension and OPEB plans are included in the tables below (in millions). Net periodic benefit costs are primarily included in “Other operation and maintenance” in the income statements.
Alliant Energy | Defined Benefit Pension Plans |  | OPEB Plans
2017 |  | 2016 |  | 2015 |  | 2017 |  | 2016 |  | 2015
Service cost |  | $12.5 |  |  |  | $12.6 |  |  |  | $15.9 |  |  |  | $5.0 |  |  |  | $5.3 |  |  |  | $5.5 |
Interest cost | 51.0 |  |  | 53.0 |  |  | 53.6 |  |  | 8.6 |  |  | 9.4 |  |  | 9.1 |
Expected return on plan assets (a) | (65.5 | ) |  | (65.5 | ) |  | (75.0 | ) |  | (6.1 | ) |  | (6.1 | ) |  | (8.4 | )
Amortization of prior service credit (b) | (0.4 | ) |  | (0.3 | ) |  | (0.2 | ) |  | (0.2 | ) |  | (4.1 | ) |  | (11.3 | )
Amortization of actuarial loss (c) | 37.6 |  |  | 37.4 |  |  | 35.4 |  |  | 3.8 |  |  | 4.7 |  |  | 4.8 |
Additional benefit costs | — |  |  | — |  |  | 0.5 |  |  | — |  |  | — |  |  | — |
Settlement losses (d) | 0.9 |  |  | — |  |  | — |  |  | — |  |  | — |  |  | — |
|  | $36.1 |  |  |  | $37.2 |  |  |  | $30.2 |  |  |  | $11.1 |  |  |  | $9.2 |  |  |  | ($0.3 | )
IPL | Defined Benefit Pension Plans |  | OPEB Plans
2017 |  | 2016 |  | 2015 |  | 2017 |  | 2016 |  | 2015
Service cost |  | $7.3 |  |  |  | $7.5 |  |  |  | $8.8 |  |  |  | $2.1 |  |  |  | $2.3 |  |  |  | $2.4 |
Interest cost | 23.5 |  |  | 24.5 |  |  | 25.0 |  |  | 3.5 |  |  | 3.8 |  |  | 3.8 |
Expected return on plan assets (a) | (30.8 | ) |  | (30.9 | ) |  | (35.8 | ) |  | (4.3 | ) |  | (4.3 | ) |  | (5.7 | )
Amortization of prior service credit (b) | (0.2 | ) |  | (0.2 | ) |  | (0.1 | ) |  | — |  |  | (2.6 | ) |  | (6.1 | )
Amortization of actuarial loss (c) | 16.1 |  |  | 16.5 |  |  | 15.3 |  |  | 2.0 |  |  | 2.6 |  |  | 2.3 |
|  | $15.9 |  |  |  | $17.4 |  |  |  | $13.2 |  |  |  | $3.3 |  |  |  | $1.8 |  |  |  | ($3.3 | )
WPL | Defined Benefit Pension Plans |  | OPEB Plans
2017 |  | 2016 |  | 2015 |  | 2017 |  | 2016 |  | 2015
Service cost |  | $4.9 |  |  |  | $4.9 |  |  |  | $5.8 |  |  |  | $1.9 |  |  |  | $2.0 |  |  |  | $2.1 |
Interest cost | 21.8 |  |  | 22.3 |  |  | 22.6 |  |  | 3.4 |  |  | 3.8 |  |  | 3.7 |
Expected return on plan assets (a) | (28.5 | ) |  | (28.3 | ) |  | (32.4 | ) |  | (0.8 | ) |  | (0.8 | ) |  | (1.5 | )
Amortization of prior service cost (credit) (b) | 0.1 |  |  | 0.2 |  |  | 0.2 |  |  | (0.2 | ) |  | (0.9 | ) |  | (3.5 | )
Amortization of actuarial loss (c) | 18.5 |  |  | 17.6 |  |  | 16.8 |  |  | 1.6 |  |  | 1.8 |  |  | 2.2 |
Additional benefit costs | — |  |  | — |  |  | 0.5 |  |  | — |  |  | — |  |  | — |
|  | $16.8 |  |  |  | $16.7 |  |  |  | $13.5 |  |  |  | $5.9 |  |  |  | $5.9 |  |  |  | $3.0 |
(a) | The expected return on plan assets is based on the expected rate of return on plan assets and the fair value approach to the market-related value of plan assets.
(b) | Unrecognized prior service costs (credits) for the OPEB plans are amortized over the average future service period to full eligibility of the participants of each plan.
(c) | Unrecognized net actuarial gains or losses in excess of 10% of the greater of the plans’ benefit obligations or assets are amortized over the average future service lives of plan participants, except for the Alliant Energy Cash Balance Pension Plan where gains or losses outside the 10% threshold are amortized over the time period the participants are expected to receive benefits.
(d) | Settlement losses related to payments made to retired executives of Alliant Energy.
Estimated Amortization From Regulatory Assets, Regulatory Liabilities And Accumulated Other Comprehensive Loss Into Net Periodic Benefit Cost | The estimated amortization from “Regulatory assets” and “Regulatory liabilities” on the balance sheets and AOCL on Alliant Energy’s balance sheet into net periodic benefit cost in 2018 is as follows (in millions):
| Alliant Energy |  | IPL |  | WPL
| Defined Benefit |  |  |  | Defined Benefit |  |  |  | Defined Benefit |  |
| Pension Plans |  | OPEB Plans |  | Pension Plans |  | OPEB Plans |  | Pension Plans |  | OPEB Plans
Actuarial loss |  | $35.2 |  |  |  | $3.4 |  |  |  | $15.0 |  |  |  | $1.2 |  |  |  | $17.2 |  |  |  | $2.0 |
Prior service credit | (0.7 | ) |  | (0.2 | ) |  | (0.2 | ) |  | — |  |  | (0.2 | ) |  | (0.2 | )
|  | $34.5 |  |  |  | $3.2 |  |  |  | $14.8 |  |  |  | $1.2 |  |  |  | $17.0 |  |  |  | $1.8 |
Funded Status Of Benefit Plans | A reconciliation of the funded status of qualified and non-qualified defined benefit pension and OPEB plans to the amounts recognized on the balance sheets at December 31 was as follows (in millions):
| Defined Benefit Pension Plans |  | OPEB Plans
Alliant Energy | 2017 |  | 2016 |  | 2017 |  | 2016
Change in benefit obligation: |  |  |  |  |  |  |
Net benefit obligation at January 1 |  | $1,244.3 |  |  |  | $1,206.3 |  |  |  | $220.1 |  |  |  | $221.4 |
Service cost | 12.5 |  |  | 12.6 |  |  | 5.0 |  |  | 5.3 |
Interest cost | 51.0 |  |  | 53.0 |  |  | 8.6 |  |  | 9.4 |
Plan participants’ contributions | — |  |  | — |  |  | 2.9 |  |  | 2.4 |
Actuarial (gain) loss | 83.6 |  |  | 48.3 |  |  | 5.4 |  |  | (0.3 | )
Gross benefits paid | (88.3 | ) |  | (75.9 | ) |  | (19.7 | ) |  | (18.1 | )
Net benefit obligation at December 31 | 1,303.1 |  |  | 1,244.3 |  |  | 222.3 |  |  | 220.1 |
Change in plan assets: |  |  |  |  |  |  |
Fair value of plan assets at January 1 | 895.7 |  |  | 895.0 |  |  | 105.8 |  |  | 106.9 |
Actual return on plan assets | 136.7 |  |  | 74.3 |  |  | 12.9 |  |  | 8.2 |
Employer contributions | 6.6 |  |  | 2.3 |  |  | 9.2 |  |  | 6.4 |
Plan participants’ contributions | — |  |  | — |  |  | 2.9 |  |  | 2.4 |
Gross benefits paid | (88.3 | ) |  | (75.9 | ) |  | (19.7 | ) |  | (18.1 | )
Fair value of plan assets at December 31 | 950.7 |  |  | 895.7 |  |  | 111.1 |  |  | 105.8 |
Under funded status at December 31 |  | ($352.4 | ) |  |  | ($348.6 | ) |  |  | ($111.2 | ) |  |  | ($114.3 | )
| Defined Benefit Pension Plans |  | OPEB Plans
Alliant Energy | 2017 |  | 2016 |  | 2017 |  | 2016
Amounts recognized on the balance sheets consist of: |  |  |  |  |  |  |
Non-current assets |  | $— |  |  |  | $— |  |  |  | $8.8 |  |  |  | $3.2 |
Current liabilities | (2.2 | ) |  | (6.5 | ) |  | (9.1 | ) |  | (8.6 | )
Pension and other benefit obligations | (350.2 | ) |  | (342.1 | ) |  | (110.9 | ) |  | (108.9 | )
Net amounts recognized at December 31 |  | ($352.4 | ) |  |  | ($348.6 | ) |  |  | ($111.2 | ) |  |  | ($114.3 | )
Amounts recognized in Regulatory Assets (refer to Note 2 for details) and AOCL (refer to Alliant Energy’s common equity statements for details) consist of: |  |  |  |  |  |  |
Net actuarial loss |  | $509.1 |  |  |  | $535.1 |  |  |  | $47.4 |  |  |  | $52.6 |
Prior service credit | (6.5 | ) |  | (6.9 | ) |  | (1.3 | ) |  | (1.5 | )
|  | $502.6 |  |  |  | $528.2 |  |  |  | $46.1 |  |  |  | $51.1 |
| Defined Benefit Pension Plans |  | OPEB Plans
IPL | 2017 |  | 2016 |  | 2017 |  | 2016
Change in benefit obligation: |  |  |  |  |  |  |
Net benefit obligation at January 1 |  | $570.4 |  |  |  | $556.1 |  |  |  | $90.1 |  |  |  | $91.3 |
Service cost | 7.3 |  |  | 7.5 |  |  | 2.1 |  |  | 2.3 |
Interest cost | 23.5 |  |  | 24.5 |  |  | 3.5 |  |  | 3.8 |
Plan participants’ contributions | — |  |  | — |  |  | 1.0 |  |  | 0.9 |
Actuarial (gain) loss | 34.9 |  |  | 19.1 |  |  | (0.1 | ) |  | (0.7 | )
Gross benefits paid | (43.2 | ) |  | (36.8 | ) |  | (7.2 | ) |  | (7.5 | )
Net benefit obligation at December 31 | 592.9 |  |  | 570.4 |  |  | 89.4 |  |  | 90.1 |
Change in plan assets: |  |  |  |  |  |  |
Fair value of plan assets at January 1 | 422.0 |  |  | 422.7 |  |  | 68.2 |  |  | 69.2 |
Actual return on plan assets | 64.3 |  |  | 35.3 |  |  | 8.9 |  |  | 5.3 |
Employer contributions | 0.6 |  |  | 0.8 |  |  | 2.0 |  |  | 0.3 |
Plan participants’ contributions | — |  |  | — |  |  | 1.0 |  |  | 0.9 |
Gross benefits paid | (43.2 | ) |  | (36.8 | ) |  | (7.2 | ) |  | (7.5 | )
Fair value of plan assets at December 31 | 443.7 |  |  | 422.0 |  |  | 72.9 |  |  | 68.2 |
Under funded status at December 31 |  | ($149.2 | ) |  |  | ($148.4 | ) |  |  | ($16.5 | ) |  |  | ($21.9 | )
| Defined Benefit Pension Plans |  | OPEB Plans
IPL | 2017 |  | 2016 |  | 2017 |  | 2016
Amounts recognized on the balance sheets consist of: |  |  |  |  |  |  |
Non-current assets |  | $— |  |  |  | $— |  |  |  | $5.9 |  |  |  | $0.4 |
Current liabilities | (0.5 | ) |  | (0.7 | ) |  | (2.0 | ) |  | (1.9 | )
Pension and other benefit obligations | (148.7 | ) |  | (147.7 | ) |  | (20.4 | ) |  | (20.4 | )
Net amounts recognized at December 31 |  | ($149.2 | ) |  |  | ($148.4 | ) |  |  | ($16.5 | ) |  |  | ($21.9 | )
Amounts recognized in Regulatory Assets consist of (refer to Note 2 for details): |  |  |  |  |  |  |
Net actuarial loss |  | $218.9 |  |  |  | $233.6 |  |  |  | $18.7 |  |  |  | $25.4 |
Prior service credit | (2.1 | ) |  | (2.3 | ) |  | — |  |  | — |
|  | $216.8 |  |  |  | $231.3 |  |  |  | $18.7 |  |  |  | $25.4 |
| Defined Benefit Pension Plans |  | OPEB Plans
WPL | 2017 |  | 2016 |  | 2017 |  | 2016
Change in benefit obligation: |  |  |  |  |  |  |
Net benefit obligation at January 1 |  | $529.2 |  |  |  | $505.9 |  |  |  | $88.9 |  |  |  | $89.7 |
Service cost | 4.9 |  |  | 4.9 |  |  | 1.9 |  |  | 2.0 |
Interest cost | 21.8 |  |  | 22.3 |  |  | 3.4 |  |  | 3.8 |
Plan participants’ contributions | — |  |  | — |  |  | 1.4 |  |  | 1.2 |
Actuarial loss | 38.3 |  |  | 25.7 |  |  | 4.1 |  |  | 0.5 |
Gross benefits paid | (34.4 | ) |  | (29.6 | ) |  | (9.3 | ) |  | (8.3 | )
Net benefit obligation at December 31 | 559.8 |  |  | 529.2 |  |  | 90.4 |  |  | 88.9 |
Change in plan assets: |  |  |  |  |  |  |
Fair value of plan assets at January 1 | 389.7 |  |  | 386.8 |  |  | 18.6 |  |  | 18.7 |
Actual return on plan assets | 59.6 |  |  | 32.4 |  |  | 1.2 |  |  | 1.2 |
Employer contributions | 0.1 |  |  | 0.1 |  |  | 6.8 |  |  | 5.8 |
Plan participants’ contributions | — |  |  | — |  |  | 1.4 |  |  | 1.2 |
Gross benefits paid | (34.4 | ) |  | (29.6 | ) |  | (9.3 | ) |  | (8.3 | )
Fair value of plan assets at December 31 | 415.0 |  |  | 389.7 |  |  | 18.7 |  |  | 18.6 |
Under funded status at December 31 |  | ($144.8 | ) |  |  | ($139.5 | ) |  |  | ($71.7 | ) |  |  | ($70.3 | )
| Defined Benefit Pension Plans |  | OPEB Plans
WPL | 2017 |  | 2016 |  | 2017 |  | 2016
Amounts recognized on the balance sheets consist of: |  |  |  |  |  |  |
Non-current assets |  | $— |  |  |  | $— |  |  |  | $2.9 |  |  |  | $2.7 |
Current liabilities | (0.1 | ) |  | (0.1 | ) |  | (6.8 | ) |  | (6.4 | )
Pension and other benefit obligations | (144.7 | ) |  | (139.4 | ) |  | (67.8 | ) |  | (66.6 | )
Net amounts recognized at December 31 |  | ($144.8 | ) |  |  | ($139.5 | ) |  |  | ($71.7 | ) |  |  | ($70.3 | )
Amounts recognized in Regulatory Assets consist of (refer to Note 2 for details): |  |  |  |  |  |  |
Net actuarial loss |  | $224.7 |  |  |  | $236.1 |  |  |  | $23.6 |  |  |  | $21.5 |
Prior service credit | (1.5 | ) |  | (1.4 | ) |  | (1.3 | ) |  | (1.5 | )
|  | $223.2 |  |  |  | $234.7 |  |  |  | $22.3 |  |  |  | $20.0 |
Accumulated Benefit Obligations | Included in the following tables are accumulated benefit obligations, aggregate amounts applicable to defined benefit pension and OPEB plans with accumulated benefit obligations in excess of plan assets, as well as defined benefit pension plans with projected benefit obligations in excess of plan assets as of the December 31 measurement date (in millions):
| Defined Benefit Pension Plans |  | OPEB Plans
Alliant Energy | 2017 |  | 2016 |  | 2017 |  | 2016
Accumulated benefit obligations |  | $1,269.0 |  |  |  | $1,201.5 |  |  |  | $222.3 |  |  |  | $220.1 |
Plans with accumulated benefit obligations in excess of plan assets: |  |  |  |  |  |  |
Accumulated benefit obligations | 1,269.0 |  |  | 1,201.5 |  |  | 222.3 |  |  | 220.1 |
Fair value of plan assets | 950.7 |  |  | 895.7 |  |  | 111.1 |  |  | 105.8 |
Plans with projected benefit obligations in excess of plan assets: |  |  |  |  |  |  |
Projected benefit obligations | 1,303.1 |  |  | 1,244.3 |  |  | N/A |  |  | N/A |
Fair value of plan assets | 950.7 |  |  | 895.7 |  |  | N/A |  |  | N/A |
| Defined Benefit Pension Plans |  | OPEB Plans
IPL | 2017 |  | 2016 |  | 2017 |  | 2016
Accumulated benefit obligations |  | $573.1 |  |  |  | $546.7 |  |  |  | $89.4 |  |  |  | $90.1 |
Plans with accumulated benefit obligations in excess of plan assets: |  |  |  |  |  |  |
Accumulated benefit obligations | 573.1 |  |  | 546.7 |  |  | 89.4 |  |  | 90.1 |
Fair value of plan assets | 443.7 |  |  | 422.0 |  |  | 72.9 |  |  | 68.2 |
Plans with projected benefit obligations in excess of plan assets: |  |  |  |  |  |  |
Projected benefit obligations | 592.9 |  |  | 570.4 |  |  | N/A |  |  | N/A |
Fair value of plan assets | 443.7 |  |  | 422.0 |  |  | N/A |  |  | N/A |
| Defined Benefit Pension Plans |  | OPEB Plans
WPL | 2017 |  | 2016 |  | 2017 |  | 2016
Accumulated benefit obligations |  | $548.1 |  |  |  | $513.2 |  |  |  | $90.4 |  |  |  | $88.9 |
Plans with accumulated benefit obligations in excess of plan assets: |  |  |  |  |  |  |
Accumulated benefit obligations | 548.1 |  |  | 513.2 |  |  | 90.4 |  |  | 88.9 |
Fair value of plan assets | 415.0 |  |  | 389.7 |  |  | 18.7 |  |  | 18.6 |
Plans with projected benefit obligations in excess of plan assets: |  |  |  |  |  |  |
Projected benefit obligations | 559.8 |  |  | 529.2 |  |  | N/A |  |  | N/A |
Fair value of plan assets | 415.0 |  |  | 389.7 |  |  | N/A |  |  | N/A |
Regulatory Assets | In addition to the amounts recognized in regulatory assets in the above tables for IPL and WPL, regulatory assets were recognized for amounts associated with Corporate Services employees participating in other Alliant Energy sponsored benefit plans that were allocated to IPL and WPL at December 31 as follows (in millions):
| IPL |  | WPL
| 2017 |  | 2016 |  | 2017 |  | 2016
Regulatory assets |  | $38.9 |  |  |  | $37.3 |  |  |  | $28.1 |  |  |  | $30.0 |
Estimated Future Employer Contributions | Estimated funding for the qualified and non-qualified defined benefit pension and OPEB plans for 2018 is as follows (in millions):
| Alliant Energy |  | IPL |  | WPL
Defined benefit pension plans (a) |  | $6.3 |  |  |  | $4.4 |  |  |  | $0.3 |
OPEB plans | 9.0 |  |  | 2.0 |  |  | 6.8 |
(a) | Alliant Energy sponsors several non-qualified defined benefit pension plans that cover certain current and former key employees of IPL and WPL. Alliant Energy allocates pension costs to IPL and WPL for these plans. In addition, IPL and WPL amounts reflect funding for their non-bargaining employees who are participants in the Alliant Energy and Corporate Services sponsored qualified and non-qualified defined benefit pension plans.
Expected Benefit Payments | Expected benefit payments for the qualified and non-qualified defined benefit plans, which reflect expected future service, as appropriate, are as follows (in millions):
Alliant Energy | 2018 |  | 2019 |  | 2020 |  | 2021 |  | 2022 |  | 2023 - 2027
Defined benefit pension benefits |  | $72.2 |  |  |  | $73.9 |  |  |  | $76.4 |  |  |  | $77.1 |  |  |  | $92.9 |  |  |  | $398.2 |
OPEB | 18.2 |  |  | 18.4 |  |  | 17.7 |  |  | 17.5 |  |  | 17.2 |  |  | 80.1 |
|  | $90.4 |  |  |  | $92.3 |  |  |  | $94.1 |  |  |  | $94.6 |  |  |  | $110.1 |  |  |  | $478.3 |
IPL | 2018 |  | 2019 |  | 2020 |  | 2021 |  | 2022 |  | 2023 - 2027
Defined benefit pension benefits |  | $33.9 |  |  |  | $33.8 |  |  |  | $36.5 |  |  |  | $36.6 |  |  |  | $37.6 |  |  |  | $188.4 |
OPEB | 7.1 |  |  | 7.1 |  |  | 7.2 |  |  | 7.1 |  |  | 7.0 |  |  | 32.6 |
|  | $41.0 |  |  |  | $40.9 |  |  |  | $43.7 |  |  |  | $43.7 |  |  |  | $44.6 |  |  |  | $221.0 |
WPL | 2018 |  | 2019 |  | 2020 |  | 2021 |  | 2022 |  | 2023 - 2027
Defined benefit pension benefits |  | $31.4 |  |  |  | $32.0 |  |  |  | $32.4 |  |  |  | $32.4 |  |  |  | $32.7 |  |  |  | $167.8 |
OPEB | 8.3 |  |  | 8.3 |  |  | 7.5 |  |  | 7.3 |  |  | 7.0 |  |  | 31.8 |
|  | $39.7 |  |  |  | $40.3 |  |  |  | $39.9 |  |  |  | $39.7 |  |  |  | $39.7 |  |  |  | $199.6 |
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 was as follows (in millions):
| Alliant Energy |  | IPL |  | WPL
| 2017 |  | 2016 |  | 2015 |  | 2017 |  | 2016 |  | 2015 |  | 2017 |  | 2016 |  | 2015
Compensation expense |  | $15.1 |  |  |  | $18.0 |  |  |  | $10.7 |  |  |  | $8.3 |  |  |  | $9.5 |  |  |  | $5.7 |  |  |  | $6.4 |  |  |  | $7.9 |  |  |  | $4.7 |
Income tax benefits | 6.2 |  |  | 7.4 |  |  | 4.4 |  |  | 3.4 |  |  | 4.0 |  |  | 2.4 |  |  | 2.6 |  |  | 3.2 |  |  | 1.9 |
Pension Plans, Defined Benefit [Member] |
Defined Benefit Plan Disclosure [Line Items] |
Fair Value Of Plan Assets By Asset Category, Fair Value Hierarchy Level and Allocations | At December 31, 2017, the current target ranges and actual allocations for the defined benefit pension plan assets were as follows:
| Target Range |  | Actual
| Allocation |  | Allocation
Cash and equivalents | 0 | % | - | 5% |  | 3%
Equity securities - U.S. | 11 | % | - | 41% |  | 24%
Equity securities - international | 14 | % | - | 34% |  | 23%
Global asset securities | 5 | % | - | 15% |  | 10%
Risk parity securities | 5 | % | - | 15% |  | 10%
Fixed income securities | 20 | % | - | 40% |  | 30%
At December 31, the fair values of qualified and non-qualified defined benefit pension plan assets were as follows (in millions):
| 2017 |  | 2016
| Fair |  | Level |  | Level |  | Level |  | Fair |  | Level |  | Level |  | Level
Alliant Energy | Value |  | 1 |  | 2 |  | 3 |  | Value |  | 1 |  | 2 |  | 3
Cash and equivalents |  | $28.2 |  |  |  | $4.5 |  |  |  | $23.7 |  |  |  | $— |  |  |  | $30.4 |  |  |  | $5.0 |  |  |  | $25.4 |  |  |  | $— |
Equity securities - U.S. | 158.3 |  |  | 158.3 |  |  | — |  |  | — |  |  | 183.6 |  |  | 183.6 |  |  | — |  |  | — |
Equity securities - international | 137.5 |  |  | 137.5 |  |  | — |  |  | — |  |  | 97.4 |  |  | 97.4 |  |  | — |  |  | — |
Global asset securities | 49.4 |  |  | 49.4 |  |  | — |  |  | — |  |  | 53.0 |  |  | 53.0 |  |  | — |  |  | — |
Fixed income securities | 135.9 |  |  | 55.8 |  |  | 80.1 |  |  | — |  |  | 125.4 |  |  | 53.6 |  |  | 71.8 |  |  | — |
Total assets in fair value hierarchy | 509.3 |  |  |  | $405.5 |  |  |  | $103.8 |  |  |  | $— |  |  | 489.8 |  |  |  | $392.6 |  |  |  | $97.2 |  |  |  | $— |
Assets measured at net asset value | 441.1 |  |  |  |  |  |  |  |  | 405.9 |  |  |  |  |  |  |
Accrued investment income | 1.0 |  |  |  |  |  |  |  |  | 1.1 |  |  |  |  |  |  |
Due to brokers, net (pending trades with brokers) | (0.7 | ) |  |  |  |  |  |  |  | (1.1 | ) |  |  |  |  |  |
Total pension plan assets |  | $950.7 |  |  |  |  |  |  |  |  |  | $895.7 |  |  |  |  |  |  |
| 2017 |  | 2016
| Fair |  | Level |  | Level |  | Level |  | Fair |  | Level |  | Level |  | Level
IPL | Value |  | 1 |  | 2 |  | 3 |  | Value |  | 1 |  | 2 |  | 3
Cash and equivalents |  | $13.2 |  |  |  | $2.2 |  |  |  | $11.0 |  |  |  | $— |  |  |  | $14.4 |  |  |  | $2.4 |  |  |  | $12.0 |  |  |  | $— |
Equity securities - U.S. | 73.9 |  |  | 73.9 |  |  | — |  |  | — |  |  | 86.5 |  |  | 86.5 |  |  | — |  |  | — |
Equity securities - international | 64.2 |  |  | 64.2 |  |  | — |  |  | — |  |  | 45.9 |  |  | 45.9 |  |  | — |  |  | — |
Global asset securities | 23.0 |  |  | 23.0 |  |  | — |  |  | — |  |  | 24.9 |  |  | 24.9 |  |  | — |  |  | — |
Fixed income securities | 63.4 |  |  | 26.0 |  |  | 37.4 |  |  | — |  |  | 59.1 |  |  | 25.3 |  |  | 33.8 |  |  | — |
Total assets in fair value hierarchy | 237.7 |  |  |  | $189.3 |  |  |  | $48.4 |  |  |  | $— |  |  | 230.8 |  |  |  | $185.0 |  |  |  | $45.8 |  |  |  | $— |
Assets measured at net asset value | 205.8 |  |  |  |  |  |  |  |  | 191.2 |  |  |  |  |  |  |
Accrued investment income | 0.5 |  |  |  |  |  |  |  |  | 0.5 |  |  |  |  |  |  |
Due to brokers, net (pending trades with brokers) | (0.3 | ) |  |  |  |  |  |  |  | (0.5 | ) |  |  |  |  |  |
Total pension plan assets |  | $443.7 |  |  |  |  |  |  |  |  |  | $422.0 |  |  |  |  |  |  |
| 2017 |  | 2016
| Fair |  | Level |  | Level |  | Level |  | Fair |  | Level |  | Level |  | Level
WPL | Value |  | 1 |  | 2 |  | 3 |  | Value |  | 1 |  | 2 |  | 3
Cash and equivalents |  | $12.3 |  |  |  | $2.0 |  |  |  | $10.3 |  |  |  | $— |  |  |  | $13.3 |  |  |  | $2.2 |  |  |  | $11.1 |  |  |  | $— |
Equity securities - U.S. | 69.1 |  |  | 69.1 |  |  | — |  |  | — |  |  | 79.9 |  |  | 79.9 |  |  | — |  |  | — |
Equity securities - international | 60.0 |  |  | 60.0 |  |  | — |  |  | — |  |  | 42.4 |  |  | 42.4 |  |  | — |  |  | — |
Global asset securities | 21.6 |  |  | 21.6 |  |  | — |  |  | — |  |  | 23.0 |  |  | 23.0 |  |  | — |  |  | — |
Fixed income securities | 59.3 |  |  | 24.3 |  |  | 35.0 |  |  | — |  |  | 54.5 |  |  | 23.3 |  |  | 31.2 |  |  | — |
Total assets in fair value hierarchy | 222.3 |  |  |  | $177.0 |  |  |  | $45.3 |  |  |  | $— |  |  | 213.1 |  |  |  | $170.8 |  |  |  | $42.3 |  |  |  | $— |
Assets measured at net asset value | 192.5 |  |  |  |  |  |  |  |  | 176.6 |  |  |  |  |  |  |
Accrued investment income | 0.5 |  |  |  |  |  |  |  |  | 0.5 |  |  |  |  |  |  |
Due to brokers, net (pending trades with brokers) | (0.3 | ) |  |  |  |  |  |  |  | (0.5 | ) |  |  |  |  |  |
Total pension plan assets |  | $415.0 |  |  |  |  |  |  |  |  |  | $389.7 |  |  |  |  |  |  |
Pension Plans, Defined Benefit [Member] | IPL [Member] |
Defined Benefit Plan Disclosure [Line Items] |
Fair Value Of Plan Assets By Asset Category, Fair Value Hierarchy Level and Allocations | At December 31, the fair values of qualified and non-qualified defined benefit pension plan assets were as follows (in millions):
| 2017 |  | 2016
| Fair |  | Level |  | Level |  | Level |  | Fair |  | Level |  | Level |  | Level
Alliant Energy | Value |  | 1 |  | 2 |  | 3 |  | Value |  | 1 |  | 2 |  | 3
Cash and equivalents |  | $28.2 |  |  |  | $4.5 |  |  |  | $23.7 |  |  |  | $— |  |  |  | $30.4 |  |  |  | $5.0 |  |  |  | $25.4 |  |  |  | $— |
Equity securities - U.S. | 158.3 |  |  | 158.3 |  |  | — |  |  | — |  |  | 183.6 |  |  | 183.6 |  |  | — |  |  | — |
Equity securities - international | 137.5 |  |  | 137.5 |  |  | — |  |  | — |  |  | 97.4 |  |  | 97.4 |  |  | — |  |  | — |
Global asset securities | 49.4 |  |  | 49.4 |  |  | — |  |  | — |  |  | 53.0 |  |  | 53.0 |  |  | — |  |  | — |
Fixed income securities | 135.9 |  |  | 55.8 |  |  | 80.1 |  |  | — |  |  | 125.4 |  |  | 53.6 |  |  | 71.8 |  |  | — |
Total assets in fair value hierarchy | 509.3 |  |  |  | $405.5 |  |  |  | $103.8 |  |  |  | $— |  |  | 489.8 |  |  |  | $392.6 |  |  |  | $97.2 |  |  |  | $— |
Assets measured at net asset value | 441.1 |  |  |  |  |  |  |  |  | 405.9 |  |  |  |  |  |  |
Accrued investment income | 1.0 |  |  |  |  |  |  |  |  | 1.1 |  |  |  |  |  |  |
Due to brokers, net (pending trades with brokers) | (0.7 | ) |  |  |  |  |  |  |  | (1.1 | ) |  |  |  |  |  |
Total pension plan assets |  | $950.7 |  |  |  |  |  |  |  |  |  | $895.7 |  |  |  |  |  |  |
| 2017 |  | 2016
| Fair |  | Level |  | Level |  | Level |  | Fair |  | Level |  | Level |  | Level
IPL | Value |  | 1 |  | 2 |  | 3 |  | Value |  | 1 |  | 2 |  | 3
Cash and equivalents |  | $13.2 |  |  |  | $2.2 |  |  |  | $11.0 |  |  |  | $— |  |  |  | $14.4 |  |  |  | $2.4 |  |  |  | $12.0 |  |  |  | $— |
Equity securities - U.S. | 73.9 |  |  | 73.9 |  |  | — |  |  | — |  |  | 86.5 |  |  | 86.5 |  |  | — |  |  | — |
Equity securities - international | 64.2 |  |  | 64.2 |  |  | — |  |  | — |  |  | 45.9 |  |  | 45.9 |  |  | — |  |  | — |
Global asset securities | 23.0 |  |  | 23.0 |  |  | — |  |  | — |  |  | 24.9 |  |  | 24.9 |  |  | — |  |  | — |
Fixed income securities | 63.4 |  |  | 26.0 |  |  | 37.4 |  |  | — |  |  | 59.1 |  |  | 25.3 |  |  | 33.8 |  |  | — |
Total assets in fair value hierarchy | 237.7 |  |  |  | $189.3 |  |  |  | $48.4 |  |  |  | $— |  |  | 230.8 |  |  |  | $185.0 |  |  |  | $45.8 |  |  |  | $— |
Assets measured at net asset value | 205.8 |  |  |  |  |  |  |  |  | 191.2 |  |  |  |  |  |  |
Accrued investment income | 0.5 |  |  |  |  |  |  |  |  | 0.5 |  |  |  |  |  |  |
Due to brokers, net (pending trades with brokers) | (0.3 | ) |  |  |  |  |  |  |  | (0.5 | ) |  |  |  |  |  |
Total pension plan assets |  | $443.7 |  |  |  |  |  |  |  |  |  | $422.0 |  |  |  |  |  |  |
| 2017 |  | 2016
| Fair |  | Level |  | Level |  | Level |  | Fair |  | Level |  | Level |  | Level
WPL | Value |  | 1 |  | 2 |  | 3 |  | Value |  | 1 |  | 2 |  | 3
Cash and equivalents |  | $12.3 |  |  |  | $2.0 |  |  |  | $10.3 |  |  |  | $— |  |  |  | $13.3 |  |  |  | $2.2 |  |  |  | $11.1 |  |  |  | $— |
Equity securities - U.S. | 69.1 |  |  | 69.1 |  |  | — |  |  | — |  |  | 79.9 |  |  | 79.9 |  |  | — |  |  | — |
Equity securities - international | 60.0 |  |  | 60.0 |  |  | — |  |  | — |  |  | 42.4 |  |  | 42.4 |  |  | — |  |  | — |
Global asset securities | 21.6 |  |  | 21.6 |  |  | — |  |  | — |  |  | 23.0 |  |  | 23.0 |  |  | — |  |  | — |
Fixed income securities | 59.3 |  |  | 24.3 |  |  | 35.0 |  |  | — |  |  | 54.5 |  |  | 23.3 |  |  | 31.2 |  |  | — |
Total assets in fair value hierarchy | 222.3 |  |  |  | $177.0 |  |  |  | $45.3 |  |  |  | $— |  |  | 213.1 |  |  |  | $170.8 |  |  |  | $42.3 |  |  |  | $— |
Assets measured at net asset value | 192.5 |  |  |  |  |  |  |  |  | 176.6 |  |  |  |  |  |  |
Accrued investment income | 0.5 |  |  |  |  |  |  |  |  | 0.5 |  |  |  |  |  |  |
Due to brokers, net (pending trades with brokers) | (0.3 | ) |  |  |  |  |  |  |  | (0.5 | ) |  |  |  |  |  |
Total pension plan assets |  | $415.0 |  |  |  |  |  |  |  |  |  | $389.7 |  |  |  |  |  |  |
At December 31, 2017, the current target ranges and actual allocations for the defined benefit pension plan assets were as follows:
| Target Range |  | Actual
| Allocation |  | Allocation
Cash and equivalents | 0 | % | - | 5% |  | 3%
Equity securities - U.S. | 11 | % | - | 41% |  | 24%
Equity securities - international | 14 | % | - | 34% |  | 23%
Global asset securities | 5 | % | - | 15% |  | 10%
Risk parity securities | 5 | % | - | 15% |  | 10%
Fixed income securities | 20 | % | - | 40% |  | 30%
Pension Plans, Defined Benefit [Member] | WPL [Member] |
Defined Benefit Plan Disclosure [Line Items] |
Fair Value Of Plan Assets By Asset Category, Fair Value Hierarchy Level and Allocations | At December 31, 2017, the current target ranges and actual allocations for the defined benefit pension plan assets were as follows:
| Target Range |  | Actual
| Allocation |  | Allocation
Cash and equivalents | 0 | % | - | 5% |  | 3%
Equity securities - U.S. | 11 | % | - | 41% |  | 24%
Equity securities - international | 14 | % | - | 34% |  | 23%
Global asset securities | 5 | % | - | 15% |  | 10%
Risk parity securities | 5 | % | - | 15% |  | 10%
Fixed income securities | 20 | % | - | 40% |  | 30%
At December 31, the fair values of qualified and non-qualified defined benefit pension plan assets were as follows (in millions):
| 2017 |  | 2016
| Fair |  | Level |  | Level |  | Level |  | Fair |  | Level |  | Level |  | Level
Alliant Energy | Value |  | 1 |  | 2 |  | 3 |  | Value |  | 1 |  | 2 |  | 3
Cash and equivalents |  | $28.2 |  |  |  | $4.5 |  |  |  | $23.7 |  |  |  | $— |  |  |  | $30.4 |  |  |  | $5.0 |  |  |  | $25.4 |  |  |  | $— |
Equity securities - U.S. | 158.3 |  |  | 158.3 |  |  | — |  |  | — |  |  | 183.6 |  |  | 183.6 |  |  | — |  |  | — |
Equity securities - international | 137.5 |  |  | 137.5 |  |  | — |  |  | — |  |  | 97.4 |  |  | 97.4 |  |  | — |  |  | — |
Global asset securities | 49.4 |  |  | 49.4 |  |  | — |  |  | — |  |  | 53.0 |  |  | 53.0 |  |  | — |  |  | — |
Fixed income securities | 135.9 |  |  | 55.8 |  |  | 80.1 |  |  | — |  |  | 125.4 |  |  | 53.6 |  |  | 71.8 |  |  | — |
Total assets in fair value hierarchy | 509.3 |  |  |  | $405.5 |  |  |  | $103.8 |  |  |  | $— |  |  | 489.8 |  |  |  | $392.6 |  |  |  | $97.2 |  |  |  | $— |
Assets measured at net asset value | 441.1 |  |  |  |  |  |  |  |  | 405.9 |  |  |  |  |  |  |
Accrued investment income | 1.0 |  |  |  |  |  |  |  |  | 1.1 |  |  |  |  |  |  |
Due to brokers, net (pending trades with brokers) | (0.7 | ) |  |  |  |  |  |  |  | (1.1 | ) |  |  |  |  |  |
Total pension plan assets |  | $950.7 |  |  |  |  |  |  |  |  |  | $895.7 |  |  |  |  |  |  |
| 2017 |  | 2016
| Fair |  | Level |  | Level |  | Level |  | Fair |  | Level |  | Level |  | Level
IPL | Value |  | 1 |  | 2 |  | 3 |  | Value |  | 1 |  | 2 |  | 3
Cash and equivalents |  | $13.2 |  |  |  | $2.2 |  |  |  | $11.0 |  |  |  | $— |  |  |  | $14.4 |  |  |  | $2.4 |  |  |  | $12.0 |  |  |  | $— |
Equity securities - U.S. | 73.9 |  |  | 73.9 |  |  | — |  |  | — |  |  | 86.5 |  |  | 86.5 |  |  | — |  |  | — |
Equity securities - international | 64.2 |  |  | 64.2 |  |  | — |  |  | — |  |  | 45.9 |  |  | 45.9 |  |  | — |  |  | — |
Global asset securities | 23.0 |  |  | 23.0 |  |  | — |  |  | — |  |  | 24.9 |  |  | 24.9 |  |  | — |  |  | — |
Fixed income securities | 63.4 |  |  | 26.0 |  |  | 37.4 |  |  | — |  |  | 59.1 |  |  | 25.3 |  |  | 33.8 |  |  | — |
Total assets in fair value hierarchy | 237.7 |  |  |  | $189.3 |  |  |  | $48.4 |  |  |  | $— |  |  | 230.8 |  |  |  | $185.0 |  |  |  | $45.8 |  |  |  | $— |
Assets measured at net asset value | 205.8 |  |  |  |  |  |  |  |  | 191.2 |  |  |  |  |  |  |
Accrued investment income | 0.5 |  |  |  |  |  |  |  |  | 0.5 |  |  |  |  |  |  |
Due to brokers, net (pending trades with brokers) | (0.3 | ) |  |  |  |  |  |  |  | (0.5 | ) |  |  |  |  |  |
Total pension plan assets |  | $443.7 |  |  |  |  |  |  |  |  |  | $422.0 |  |  |  |  |  |  |
| 2017 |  | 2016
| Fair |  | Level |  | Level |  | Level |  | Fair |  | Level |  | Level |  | Level
WPL | Value |  | 1 |  | 2 |  | 3 |  | Value |  | 1 |  | 2 |  | 3
Cash and equivalents |  | $12.3 |  |  |  | $2.0 |  |  |  | $10.3 |  |  |  | $— |  |  |  | $13.3 |  |  |  | $2.2 |  |  |  | $11.1 |  |  |  | $— |
Equity securities - U.S. | 69.1 |  |  | 69.1 |  |  | — |  |  | — |  |  | 79.9 |  |  | 79.9 |  |  | — |  |  | — |
Equity securities - international | 60.0 |  |  | 60.0 |  |  | — |  |  | — |  |  | 42.4 |  |  | 42.4 |  |  | — |  |  | — |
Global asset securities | 21.6 |  |  | 21.6 |  |  | — |  |  | — |  |  | 23.0 |  |  | 23.0 |  |  | — |  |  | — |
Fixed income securities | 59.3 |  |  | 24.3 |  |  | 35.0 |  |  | — |  |  | 54.5 |  |  | 23.3 |  |  | 31.2 |  |  | — |
Total assets in fair value hierarchy | 222.3 |  |  |  | $177.0 |  |  |  | $45.3 |  |  |  | $— |  |  | 213.1 |  |  |  | $170.8 |  |  |  | $42.3 |  |  |  | $— |
Assets measured at net asset value | 192.5 |  |  |  |  |  |  |  |  | 176.6 |  |  |  |  |  |  |
Accrued investment income | 0.5 |  |  |  |  |  |  |  |  | 0.5 |  |  |  |  |  |  |
Due to brokers, net (pending trades with brokers) | (0.3 | ) |  |  |  |  |  |  |  | (0.5 | ) |  |  |  |  |  |
Total pension plan assets |  | $415.0 |  |  |  |  |  |  |  |  |  | $389.7 |  |  |  |  |  |  |
Other Postretirement Benefits Plans [Member] |
Defined Benefit Plan Disclosure [Line Items] |
Fair Value Of Plan Assets By Asset Category, Fair Value Hierarchy Level and Allocations | At December 31, 2017, the current target ranges and actual allocations for VEBA trusts with assets greater than $5 million and the WPL 401(h) assets were as follows:
| Target Range |  | Actual
| Allocation |  | Allocation
Cash and equivalents | 0 | % | - | 5% |  | 1%
Equity securities - U.S. | 0 | % | - | 50% |  | 26%
Equity securities - international | 0 | % | - | 34% |  | 10%
Fixed income securities | 20 | % | - | 100% |  | 63%
At December 31, the fair values of OPEB plan assets were as follows (in millions):
| 2017 |  | 2016
| Fair |  | Level |  | Level |  | Level |  | Fair |  | Level |  | Level |  | Level
Alliant Energy | Value |  | 1 |  | 2 |  | 3 |  | Value |  | 1 |  | 2 |  | 3
Cash and equivalents |  | $1.2 |  |  |  | $0.7 |  |  |  | $0.5 |  |  |  | $— |  |  |  | $3.5 |  |  |  | $2.0 |  |  |  | $1.5 |  |  |  | $— |
Equity securities - U.S. | 27.9 |  |  | 27.9 |  |  | — |  |  | — |  |  | 22.5 |  |  | 22.5 |  |  | — |  |  | — |
Equity securities - international | 11.4 |  |  | 11.4 |  |  | — |  |  | — |  |  | 13.5 |  |  | 13.5 |  |  | — |  |  | — |
Global asset securities | 0.4 |  |  | 0.4 |  |  | — |  |  | — |  |  | 16.5 |  |  | 16.5 |  |  | — |  |  | — |
Fixed income securities | 66.6 |  |  | 66.0 |  |  | 0.6 |  |  | — |  |  | 46.8 |  |  | 46.2 |  |  | 0.6 |  |  | — |
Total assets in fair value hierarchy | 107.5 |  |  |  | $106.4 |  |  |  | $1.1 |  |  |  | $— |  |  | 102.8 |  |  |  | $100.7 |  |  |  | $2.1 |  |  |  | $— |
Assets measured at net asset value | 3.6 |  |  |  |  |  |  |  |  | 3.0 |  |  |  |  |  |  |
Total OPEB plan assets |  | $111.1 |  |  |  |  |  |  |  |  |  | $105.8 |  |  |  |  |  |  |
| 2017 |  | 2016
| Fair |  | Level |  | Level |  | Level |  | Fair |  | Level |  | Level |  | Level
IPL | Value |  | 1 |  | 2 |  | 3 |  | Value |  | 1 |  | 2 |  | 3
Cash and equivalents |  | $0.3 |  |  |  | $0.3 |  |  |  | $— |  |  |  | $— |  |  |  | $0.8 |  |  |  | $0.8 |  |  |  | $— |  |  |  | $— |
Equity securities - U.S. | 22.3 |  |  | 22.3 |  |  | — |  |  | — |  |  | 17.0 |  |  | 17.0 |  |  | — |  |  | — |
Equity securities - international | 7.5 |  |  | 7.5 |  |  | — |  |  | — |  |  | 11.0 |  |  | 11.0 |  |  | — |  |  | — |
Global asset securities | — |  |  | — |  |  | — |  |  | — |  |  | 7.0 |  |  | 7.0 |  |  | — |  |  | — |
Fixed income securities | 42.8 |  |  | 42.8 |  |  | — |  |  | — |  |  | 32.4 |  |  | 32.4 |  |  | — |  |  | — |
Total OPEB plan assets |  | $72.9 |  |  |  | $72.9 |  |  |  | $— |  |  |  | $— |  |  |  | $68.2 |  |  |  | $68.2 |  |  |  | $— |  |  |  | $— |
| 2017 |  | 2016
| Fair |  | Level |  | Level |  | Level |  | Fair |  | Level |  | Level |  | Level
WPL | Value |  | 1 |  | 2 |  | 3 |  | Value |  | 1 |  | 2 |  | 3
Cash and equivalents |  | $0.6 |  |  |  | $0.3 |  |  |  | $0.3 |  |  |  | $— |  |  |  | $2.0 |  |  |  | $0.7 |  |  |  | $1.3 |  |  |  | $— |
Global asset securities | — |  |  | — |  |  | — |  |  | — |  |  | 5.5 |  |  | 5.5 |  |  | — |  |  | — |
Fixed income securities | 18.1 |  |  | 18.1 |  |  | — |  |  | — |  |  | 11.1 |  |  | 11.1 |  |  | — |  |  | — |
Total OPEB plan assets |  | $18.7 |  |  |  | $18.4 |  |  |  | $0.3 |  |  |  | $— |  |  |  | $18.6 |  |  |  | $17.3 |  |  |  | $1.3 |  |  |  | $— |
Other Postretirement Benefits Plans [Member] | IPL [Member] |
Defined Benefit Plan Disclosure [Line Items] |
Fair Value Of Plan Assets By Asset Category, Fair Value Hierarchy Level and Allocations | At December 31, 2017, the current target ranges and actual allocations for VEBA trusts with assets greater than $5 million and the WPL 401(h) assets were as follows:
| Target Range |  | Actual
| Allocation |  | Allocation
Cash and equivalents | 0 | % | - | 5% |  | 1%
Equity securities - U.S. | 0 | % | - | 50% |  | 26%
Equity securities - international | 0 | % | - | 34% |  | 10%
Fixed income securities | 20 | % | - | 100% |  | 63%
At December 31, the fair values of OPEB plan assets were as follows (in millions):
| 2017 |  | 2016
| Fair |  | Level |  | Level |  | Level |  | Fair |  | Level |  | Level |  | Level
Alliant Energy | Value |  | 1 |  | 2 |  | 3 |  | Value |  | 1 |  | 2 |  | 3
Cash and equivalents |  | $1.2 |  |  |  | $0.7 |  |  |  | $0.5 |  |  |  | $— |  |  |  | $3.5 |  |  |  | $2.0 |  |  |  | $1.5 |  |  |  | $— |
Equity securities - U.S. | 27.9 |  |  | 27.9 |  |  | — |  |  | — |  |  | 22.5 |  |  | 22.5 |  |  | — |  |  | — |
Equity securities - international | 11.4 |  |  | 11.4 |  |  | — |  |  | — |  |  | 13.5 |  |  | 13.5 |  |  | — |  |  | — |
Global asset securities | 0.4 |  |  | 0.4 |  |  | — |  |  | — |  |  | 16.5 |  |  | 16.5 |  |  | — |  |  | — |
Fixed income securities | 66.6 |  |  | 66.0 |  |  | 0.6 |  |  | — |  |  | 46.8 |  |  | 46.2 |  |  | 0.6 |  |  | — |
Total assets in fair value hierarchy | 107.5 |  |  |  | $106.4 |  |  |  | $1.1 |  |  |  | $— |  |  | 102.8 |  |  |  | $100.7 |  |  |  | $2.1 |  |  |  | $— |
Assets measured at net asset value | 3.6 |  |  |  |  |  |  |  |  | 3.0 |  |  |  |  |  |  |
Total OPEB plan assets |  | $111.1 |  |  |  |  |  |  |  |  |  | $105.8 |  |  |  |  |  |  |
| 2017 |  | 2016
| Fair |  | Level |  | Level |  | Level |  | Fair |  | Level |  | Level |  | Level
IPL | Value |  | 1 |  | 2 |  | 3 |  | Value |  | 1 |  | 2 |  | 3
Cash and equivalents |  | $0.3 |  |  |  | $0.3 |  |  |  | $— |  |  |  | $— |  |  |  | $0.8 |  |  |  | $0.8 |  |  |  | $— |  |  |  | $— |
Equity securities - U.S. | 22.3 |  |  | 22.3 |  |  | — |  |  | — |  |  | 17.0 |  |  | 17.0 |  |  | — |  |  | — |
Equity securities - international | 7.5 |  |  | 7.5 |  |  | — |  |  | — |  |  | 11.0 |  |  | 11.0 |  |  | — |  |  | — |
Global asset securities | — |  |  | — |  |  | — |  |  | — |  |  | 7.0 |  |  | 7.0 |  |  | — |  |  | — |
Fixed income securities | 42.8 |  |  | 42.8 |  |  | — |  |  | — |  |  | 32.4 |  |  | 32.4 |  |  | — |  |  | — |
Total OPEB plan assets |  | $72.9 |  |  |  | $72.9 |  |  |  | $— |  |  |  | $— |  |  |  | $68.2 |  |  |  | $68.2 |  |  |  | $— |  |  |  | $— |
| 2017 |  | 2016
| Fair |  | Level |  | Level |  | Level |  | Fair |  | Level |  | Level |  | Level
WPL | Value |  | 1 |  | 2 |  | 3 |  | Value |  | 1 |  | 2 |  | 3
Cash and equivalents |  | $0.6 |  |  |  | $0.3 |  |  |  | $0.3 |  |  |  | $— |  |  |  | $2.0 |  |  |  | $0.7 |  |  |  | $1.3 |  |  |  | $— |
Global asset securities | — |  |  | — |  |  | — |  |  | — |  |  | 5.5 |  |  | 5.5 |  |  | — |  |  | — |
Fixed income securities | 18.1 |  |  | 18.1 |  |  | — |  |  | — |  |  | 11.1 |  |  | 11.1 |  |  | — |  |  | — |
Total OPEB plan assets |  | $18.7 |  |  |  | $18.4 |  |  |  | $0.3 |  |  |  | $— |  |  |  | $18.6 |  |  |  | $17.3 |  |  |  | $1.3 |  |  |  | $— |
Other Postretirement Benefits Plans [Member] | WPL [Member] |
Defined Benefit Plan Disclosure [Line Items] |
Fair Value Of Plan Assets By Asset Category, Fair Value Hierarchy Level and Allocations | At December 31, the fair values of OPEB plan assets were as follows (in millions):
| 2017 |  | 2016
| Fair |  | Level |  | Level |  | Level |  | Fair |  | Level |  | Level |  | Level
Alliant Energy | Value |  | 1 |  | 2 |  | 3 |  | Value |  | 1 |  | 2 |  | 3
Cash and equivalents |  | $1.2 |  |  |  | $0.7 |  |  |  | $0.5 |  |  |  | $— |  |  |  | $3.5 |  |  |  | $2.0 |  |  |  | $1.5 |  |  |  | $— |
Equity securities - U.S. | 27.9 |  |  | 27.9 |  |  | — |  |  | — |  |  | 22.5 |  |  | 22.5 |  |  | — |  |  | — |
Equity securities - international | 11.4 |  |  | 11.4 |  |  | — |  |  | — |  |  | 13.5 |  |  | 13.5 |  |  | — |  |  | — |
Global asset securities | 0.4 |  |  | 0.4 |  |  | — |  |  | — |  |  | 16.5 |  |  | 16.5 |  |  | — |  |  | — |
Fixed income securities | 66.6 |  |  | 66.0 |  |  | 0.6 |  |  | — |  |  | 46.8 |  |  | 46.2 |  |  | 0.6 |  |  | — |
Total assets in fair value hierarchy | 107.5 |  |  |  | $106.4 |  |  |  | $1.1 |  |  |  | $— |  |  | 102.8 |  |  |  | $100.7 |  |  |  | $2.1 |  |  |  | $— |
Assets measured at net asset value | 3.6 |  |  |  |  |  |  |  |  | 3.0 |  |  |  |  |  |  |
Total OPEB plan assets |  | $111.1 |  |  |  |  |  |  |  |  |  | $105.8 |  |  |  |  |  |  |
| 2017 |  | 2016
| Fair |  | Level |  | Level |  | Level |  | Fair |  | Level |  | Level |  | Level
IPL | Value |  | 1 |  | 2 |  | 3 |  | Value |  | 1 |  | 2 |  | 3
Cash and equivalents |  | $0.3 |  |  |  | $0.3 |  |  |  | $— |  |  |  | $— |  |  |  | $0.8 |  |  |  | $0.8 |  |  |  | $— |  |  |  | $— |
Equity securities - U.S. | 22.3 |  |  | 22.3 |  |  | — |  |  | — |  |  | 17.0 |  |  | 17.0 |  |  | — |  |  | — |
Equity securities - international | 7.5 |  |  | 7.5 |  |  | — |  |  | — |  |  | 11.0 |  |  | 11.0 |  |  | — |  |  | — |
Global asset securities | — |  |  | — |  |  | — |  |  | — |  |  | 7.0 |  |  | 7.0 |  |  | — |  |  | — |
Fixed income securities | 42.8 |  |  | 42.8 |  |  | — |  |  | — |  |  | 32.4 |  |  | 32.4 |  |  | — |  |  | — |
Total OPEB plan assets |  | $72.9 |  |  |  | $72.9 |  |  |  | $— |  |  |  | $— |  |  |  | $68.2 |  |  |  | $68.2 |  |  |  | $— |  |  |  | $— |
| 2017 |  | 2016
| Fair |  | Level |  | Level |  | Level |  | Fair |  | Level |  | Level |  | Level
WPL | Value |  | 1 |  | 2 |  | 3 |  | Value |  | 1 |  | 2 |  | 3
Cash and equivalents |  | $0.6 |  |  |  | $0.3 |  |  |  | $0.3 |  |  |  | $— |  |  |  | $2.0 |  |  |  | $0.7 |  |  |  | $1.3 |  |  |  | $— |
Global asset securities | — |  |  | — |  |  | — |  |  | — |  |  | 5.5 |  |  | 5.5 |  |  | — |  |  | — |
Fixed income securities | 18.1 |  |  | 18.1 |  |  | — |  |  | — |  |  | 11.1 |  |  | 11.1 |  |  | — |  |  | — |
Total OPEB plan assets |  | $18.7 |  |  |  | $18.4 |  |  |  | $0.3 |  |  |  | $— |  |  |  | $18.6 |  |  |  | $17.3 |  |  |  | $1.3 |  |  |  | $— |
At December 31, 2017, the current target ranges and actual allocations for VEBA trusts with assets greater than $5 million and the WPL 401(h) assets were as follows:
| Target Range |  | Actual
| Allocation |  | Allocation
Cash and equivalents | 0 | % | - | 5% |  | 1%
Equity securities - U.S. | 0 | % | - | 50% |  | 26%
Equity securities - international | 0 | % | - | 34% |  | 10%
Fixed income securities | 20 | % | - | 100% |  | 63%
401(k) Savings Plan [Member] |
Defined Benefit Plan Disclosure [Line Items] |
Employees Participate In Defined Contribution Retirement Plans | 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
| 2017 |  | 2016 |  | 2015 |  | 2017 |  |  | 2016 |  |  | 2015 |  |  | 2017 |  | 2016 |  | 2015
401(k) costs |  | $24.8 |  |  |  | $23.6 |  |  |  | $24.9 |  |  |  | $12.8 |  |  |  | $12.0 |  |  |  | $12.7 |  |  |  | $11.1 |  |  |  | $10.7 |  |  |  | $11.2 |
401(k) Savings Plan [Member] | IPL [Member] |
Defined Benefit Plan Disclosure [Line Items] |
Employees Participate In Defined Contribution Retirement Plans | 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
| 2017 |  | 2016 |  | 2015 |  | 2017 |  |  | 2016 |  |  | 2015 |  |  | 2017 |  | 2016 |  | 2015
401(k) costs |  | $24.8 |  |  |  | $23.6 |  |  |  | $24.9 |  |  |  | $12.8 |  |  |  | $12.0 |  |  |  | $12.7 |  |  |  | $11.1 |  |  |  | $10.7 |  |  |  | $11.2 |
401(k) Savings Plan [Member] | WPL [Member] |
Defined Benefit Plan Disclosure [Line Items] |
Employees Participate In Defined Contribution Retirement Plans | 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
| 2017 |  | 2016 |  | 2015 |  | 2017 |  |  | 2016 |  |  | 2015 |  |  | 2017 |  | 2016 |  | 2015
401(k) costs |  | $24.8 |  |  |  | $23.6 |  |  |  | $24.9 |  |  |  | $12.8 |  |  |  | $12.0 |  |  |  | $12.7 |  |  |  | $11.1 |  |  |  | $10.7 |  |  |  | $11.2 |
Performance Shares and Performance Units [Member] |
Defined Benefit Plan Disclosure [Line Items] |
Schedule Of Equity-based Compensation Plans Activity | 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 |  | 2015 |  | 2017 |  | 2016 |  | 2015
Nonvested awards, January 1 | 257,599 |  |  | 288,430 |  |  | 288,848 |  |  | 93,320 |  |  | 116,412 |  |  | 127,330 |
Granted | 65,350 |  |  | 68,585 |  |  | 90,806 |  |  | 21,558 |  |  | 23,918 |  |  | 35,674 |
Vested | (99,438 | ) |  | (98,186 | ) |  | (91,224 | ) |  | (37,395 | ) |  | (42,760 | ) |  | (45,690 | )
Forfeited | — |  |  | (1,230 | ) |  | — |  |  | (5,746 | ) |  | (4,250 | ) |  | (902 | )
Nonvested awards, December 31 | 223,511 |  |  | 257,599 |  |  | 288,430 |  |  | 71,737 |  |  | 93,320 |  |  | 116,412 |
Granted Awards - Each performance share’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 performance units granted in 2017 and 2016, the 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 performance units granted in 2015, the value is based on the closing market price of one share of Alliant Energy’s common stock on the grant date of the award. The actual payout for performance shares and performance units is dependent upon actual performance and may range from zero to 200% of the target number of awards. Compensation expense for performance shares and performance units is recorded ratably over the performance period based on the fair value of the awards at each reporting period. Vested Awards - 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 |  | 2015 |  | 2017 |  | 2016 |  | 2015
| 2014 Grant |  | 2013 Grant |  | 2012 Grant |  | 2014 Grant |  | 2013 Grant |  | 2012 Grant
Performance awards vested | 99,438 |  | 98,186 |  | 91,224 |  | 37,395 |  | 42,760 |  | 45,690
Percentage of target number of performance awards | 147.5% |  | 165.0% |  | 167.5% |  | 147.5% |  | 165.0% |  | 167.5%
Aggregate payout value (in millions) | $5.6 |  | $5.1 |  | $5.1 |  | $1.5 |  | $1.7 |  | $1.6
Payout - cash (in millions) | $5.1 |  | $2.9 |  | $3.2 |  | $1.5 |  | $1.7 |  | $1.6
Payout - common stock shares issued | 5,185 |  | 22,408 |  | 21,950 |  | N/A |  | N/A |  | N/A
Fair Value of Awards - Information related to fair values of nonvested performance shares and performance units at December 31, 2017, by year of grant, were as follows:
| Performance Shares |  | Performance Units
| 2017 Grant |  | 2016 Grant |  | 2015 Grant |  | 2017 Grant |  | 2016 Grant |  | 2015 Grant
Nonvested awards at target | 65,350 |  |  | 67,355 |  |  | 90,806 |  |  | 18,600 |  |  | 21,227 |  |  | 31,910 |
Alliant Energy common stock closing price on December 29, 2017 |  | $42.61 |  |  |  | $42.61 |  |  |  | $42.61 |  |  |  | $42.61 |  |  |  | $42.61 |  |  | 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 | 105 | % |  | 150 | % |  | 138 | % |  | 105 | % |  | 150 | % |  | 138 | %
Fair values of each nonvested award |  | $44.74 |  |  |  | $63.92 |  |  |  | $58.80 |  |  |  | $44.74 |  |  |  | $63.92 |  |  |  | $44.92 |
Performance Restricted Stock Unit [Member] |
Defined Benefit Plan Disclosure [Line Items] |
Schedule Of Equity-based Compensation Plans Activity | 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 | 65,350 |  |  | 39.12 |  |  | 68,585 |  |  | 33.96 |
Forfeited | — |  |  | — |  |  | (1,230 | ) |  | 33.90 |
Nonvested units, December 31 | 132,705 |  |  | 36.50 |  |  | 67,355 |  |  | 33.96 |
Restricted Stock Units [Member] |
Defined Benefit Plan Disclosure [Line Items] |
Schedule Of Equity-based Compensation Plans Activity | A summary of the restricted stock units activity was as follows:
| 2017 |  | 2016
Nonvested units, January 1 | 57,736 |  |  | — |
Granted | 56,013 |  |  | 58,790 |
Forfeited | — |  |  | (1,054 | )
Nonvested units, December 31 | 113,749 |  |  | 57,736 |

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- Definition Tabular disclosure of the assumptions used to determine for pension plans and/or other employee benefit plans the benefit obligation and net benefit cost, including assumed discount rates, rate increase in compensation increase, and expected long-term rates of return on plan assets. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (k) -URI http://asc.fasb.org/extlink&oid=65897934&loc=d3e1928-114920 + Details
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