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Employee Benefits - Assumptions (Details) - USD ($) $ in Millions | 12 Months Ended
--- | ---
Dec. 31, 2016 | Dec. 31, 2015 | Dec. 31, 2014
Pension Benefits |  |  |
Weighted average assumptions used |  |  |
Discount rate | 4.16% | 4.46% |
Rate of compensation increase | 3.60% | 4.00% |
Discount rate | 4.35% | 4.11% | 5.00%
Expected return on plan assets | 7.12% | 7.37% | 7.25%
Rate of compensation increase | 3.75% | 4.00% | 4.00%
Expected return on assets during next fiscal year | 7.11% |  |
OPEB |  |  |
Weighted average assumptions used |  |  |
Discount rate | 4.14% | 4.38% |
Assumed medical cost trend rate (as a percent) | 7.00% | 7.50% |
Ultimate trend rate (as a percent) | 5.00% | 5.00% |
Year ultimate trend rate is reached | 2021 | 2021 |
Discount rate | 4.38% | 4.09% | 4.95%
Expected return on plan assets | 7.25% | 7.54% | 7.50%
Expected return on assets during next fiscal year | 7.25% |  |
Effects of a one-percentage-point change in assumed health care cost trend rates |  |  |
Effect of one-percentage-point increase on total of service and interest cost components of net periodic postretirement health care benefit cost | $ 8.5 |  |
Effect of one-percentage-point decrease on total of service and interest cost components of net periodic postretirement health care benefit cost | (6.9) |  |
Effect of one-percentage-point increase on the health care component of the accumulated postretirement benefit obligation | 49.6 |  |
Effect of one-percentage-point decrease on the health care component of the accumulated postretirement benefit obligation | $ (39.5) |  |
OPEB | Maximum |  |  |
Weighted average assumptions used |  |  |
Assumed medical cost trend rate (as a percent) | 7.50% | 7.50% | 7.50%
Ultimate trend rate (as a percent) | 5.00% | 5.00% | 5.00%
Year ultimate trend rate is reached | 2021 | 2021 | 2021
Wisconsin Energy | Pension Benefits | Equity securities: |  |  |
Target asset allocations |  |  |
Target asset allocations (as a percent) | 35.00% |  |
Wisconsin Energy | Pension Benefits | Fixed income securities: |  |  |
Target asset allocations |  |  |
Target asset allocations (as a percent) | 55.00% |  |
Wisconsin Energy | Pension Benefits | Private equity funds |  |  |
Target asset allocations |  |  |
Target asset allocations (as a percent) | 10.00% |  |
Wisconsin Energy | OPEB | Equity securities: |  |  |
Target asset allocations |  |  |
Target asset allocations (as a percent) | 60.00% |  |
Wisconsin Energy | OPEB | Fixed income securities: |  |  |
Target asset allocations |  |  |
Target asset allocations (as a percent) | 40.00% |  |
Integrys Holding Inc | Pension Benefits | Equity securities: |  |  |
Target asset allocations |  |  |
Target asset allocations (as a percent) | 60.00% |  |
Integrys Holding Inc | Pension Benefits | Fixed income securities: |  |  |
Target asset allocations |  |  |
Target asset allocations (as a percent) | 40.00% |  |
Integrys Holding Inc | OPEB | Equity securities: |  |  |
Target asset allocations |  |  |
Target asset allocations (as a percent) | 45.00% |  |
Integrys Holding Inc | OPEB | Equity securities: | Maximum |  |  |
Target asset allocations |  |  |
Target asset allocations (as a percent) | 50.00% |  |
Integrys Holding Inc | OPEB | Fixed income securities: |  |  |
Target asset allocations |  |  |
Target asset allocations (as a percent) | 50.00% |  |
Integrys Holding Inc | OPEB | Fixed income securities: | Maximum |  |  |
Target asset allocations |  |  |
Target asset allocations (as a percent) | 55.00% |  |

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- Definition The interest rate used to adjust for the time value of money for the plan. + 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)(1) -URI http://asc.fasb.org/extlink&oid=65897934&loc=d3e1928-114920 + Details
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- Definition Expected rate of compensation increases (for pay-related plans). + 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)(2) -URI http://asc.fasb.org/extlink&oid=65897934&loc=d3e1928-114920 + Details
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- Definition An assumption as to the rate of return on plan assets reflecting the average rate of earnings expected on the funds invested or to be invested to provide for the benefits included in the benefit obligation. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Glossary Expected Long-Term Rate of Return on Plan Assets -URI http://asc.fasb.org/extlink&oid=6512046 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (k)(3) -URI http://asc.fasb.org/extlink&oid=65897934&loc=d3e1928-114920 + Details
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- Definition Expected rate of compensation increases (for pay-related plans). + 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)(2) -URI http://asc.fasb.org/extlink&oid=65897934&loc=d3e1928-114920 + Details
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- Definition The assumed health care cost trend rate for the next year used to measure the expected cost of benefits covered by the plan (gross eligible charges). This is based upon the annual rate of change in the cost of health care benefits currently provided by the postretirement benefit plan, due to factors other than changes in the composition of the plan population by age and dependency status. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Glossary Health Care Cost Trend Rate -URI http://asc.fasb.org/extlink&oid=6514820 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (l) -URI http://asc.fasb.org/extlink&oid=65897934&loc=d3e1928-114920 + Details
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