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REGULATORY ENVIRONMENT (Details) $ in Millions | 1 Months Ended
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Apr. 30, 2017 USD ($) | Mar. 31, 2017 USD ($) | Jan. 31, 2017 | Oct. 31, 2016 USD ($) | Aug. 31, 2016 USD ($) MW | Apr. 30, 2015 USD ($)
WE, WG, and WPS | Natural gas storage facility in Michigan |  |  |  |  |  |
Regulatory environment |  |  |  |  |  |
Percentage of natural gas storage needs provided by the facility |  |  | 33.33% |  |  |
PGL | Illinois Commerce Commission (ICC) |  |  |  |  |  |
Regulatory environment |  |  |  |  |  |
Number of years code of conduct reports must be provided to the ICC |  | 4 years |  |  |  |
Number of years quality assurance reports must be provided to the ICC |  | 4 years |  |  |  |
Amount of assurance that PGL's QIP rider costs will be recoverable |  | 0 |  |  |  |
MERC | Minnesota Public Utilities Commission (MPUC) | 2016 rates | Natural gas rates |  |  |  |  |  |
Regulatory environment |  |  |  |  |  |
Approved rate increase |  |  |  | $ 6.8 |  |
Approved rate increase (as a percent) |  |  |  | 3.00% |  |
Approved return on equity (as a percent) |  |  |  | 9.11% |  |
Approved common equity component average (as a percent) |  |  |  | 50.32% |  |
Number of years decoupling mechanism authorized for use |  |  |  | 3 years |  |
Interim rate refund |  | $ 4.1 |  |  |  |
UMERC |  |  |  |  |  |
Regulatory environment |  |  |  |  |  |
Term of electric power purchase agreement (in years) |  |  |  |  | 20 years |
Capacity of natural gas-fired generation facility (in megawatts) | MW |  |  |  |  | 180 |
Estimated cost of constructing a power plant |  |  |  |  | $ 265.0 |
Estimated cost of constructing a power plant, including AFUDC |  |  |  |  | $ 275.0 |
Portion of the power plant costs recoverable from Tilden Mining Company (as a percent) |  |  |  |  | 50.00% |
Portion of the power plant costs recoverable from utility customers (as a percent) |  |  |  |  | 50.00% |
UMERC | Michigan Public Service Commission (MPSC) | 2015 rates | Electric rates |  |  |  |  |  |
Regulatory environment |  |  |  |  |  |
Approved rate increase |  |  |  |  |  | $ 4.0
Approved return on equity (as a percent) |  |  |  |  |  | 10.20%
Approved common equity component average (as a percent) |  |  |  |  |  | 50.48%
Period of rate implementation (in years) |  |  |  |  |  | 3 years
Subsequent event | WE, WG, and WPS | Public Service Commission of Wisconsin (PSCW) | 2018 and 2019 rates |  |  |  |  |  |
Regulatory environment |  |  |  |  |  |
Authorized revenue requirement for ReACT | $ 275.0 |  |  |  |  |
Number of utilities with earnings sharing mechanism | 3 |  |  |  |  |
Percentage of first 50 basis points of additional utility earnings shared with customers | 50.00% |  |  |  |  |
ROE in excess of authorized amount (as a percent) | 0.50% |  |  |  |  |

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