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Employee Benefits - Target Asset Allocations (Details) | Dec. 31, 2017
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Pension Plan | Wisconsin Energy Corporation | Equity securities |
Defined Benefit Plan Disclosure [Line Items] |
Target asset allocations (as a percent) | 35.00%
Pension Plan | Wisconsin Energy Corporation | Fixed income securities |
Defined Benefit Plan Disclosure [Line Items] |
Target asset allocations (as a percent) | 55.00%
Pension Plan | Wisconsin Energy Corporation | Private equity and real estate |
Defined Benefit Plan Disclosure [Line Items] |
Target asset allocations (as a percent) | 10.00%
Pension Plan | Integrys Holding Inc | Equity securities |
Defined Benefit Plan Disclosure [Line Items] |
Target asset allocations (as a percent) | 45.00%
Pension Plan | Integrys Holding Inc | Fixed income securities |
Defined Benefit Plan Disclosure [Line Items] |
Target asset allocations (as a percent) | 45.00%
Pension Plan | Integrys Holding Inc | Private equity and real estate |
Defined Benefit Plan Disclosure [Line Items] |
Target asset allocations (as a percent) | 10.00%
OPEB Plan | Wisconsin Energy Corporation | Equity securities |
Defined Benefit Plan Disclosure [Line Items] |
Target asset allocations (as a percent) | 60.00%
OPEB Plan | Wisconsin Energy Corporation | Fixed income securities |
Defined Benefit Plan Disclosure [Line Items] |
Target asset allocations (as a percent) | 40.00%
OPEB Plan | Integrys Holding Inc | Largest trust 1 | Equity securities |
Defined Benefit Plan Disclosure [Line Items] |
Target asset allocations (as a percent) | 45.00%
OPEB Plan | Integrys Holding Inc | Largest trust 1 | Fixed income securities |
Defined Benefit Plan Disclosure [Line Items] |
Target asset allocations (as a percent) | 55.00%
OPEB Plan | Integrys Holding Inc | Largest trust 2 | Equity securities |
Defined Benefit Plan Disclosure [Line Items] |
Target asset allocations (as a percent) | 50.00%
OPEB Plan | Integrys Holding Inc | Largest trust 2 | Fixed income securities |
Defined Benefit Plan Disclosure [Line Items] |
Target asset allocations (as a percent) | 50.00%

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- Definition Percentage of target investment allocation to total plan assets. Includes, but is not limited to, percentage on weighted-average basis if more than one 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 (d)(5)(i) -URI http://asc.fasb.org/extlink&oid=82843861&loc=d3e1928-114920 + Details
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