Employee Benefits - Target Asset Allocations (Details)	Dec. 31, 2019
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 | Largest trust 1 | Equity securities
Defined Benefit Plan Disclosure [Line Items]
Target asset allocations (as a percent)	50.00%
OPEB Plan | Wisconsin Energy Corporation | Largest trust 1 | Fixed income securities
Defined Benefit Plan Disclosure [Line Items]
Target asset allocations (as a percent)	50.00%
OPEB Plan | Wisconsin Energy Corporation | Largest trust 2 | Equity securities
Defined Benefit Plan Disclosure [Line Items]
Target asset allocations (as a percent)	70.00%
OPEB Plan | Wisconsin Energy Corporation | Largest trust 2 | Fixed income securities
Defined Benefit Plan Disclosure [Line Items]
Target asset allocations (as a percent)	30.00%
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)	45.00%
OPEB Plan | Integrys Holding Inc | Largest trust 2 | Fixed income securities
Defined Benefit Plan Disclosure [Line Items]
Target asset allocations (as a percent)	55.00%