REGULATORY ENVIRONMENT (Details) $ in Millions	1 Months Ended								3 Months Ended	6 Months Ended
	May 31, 2018 USD ($) MW solar_projects	Mar. 31, 2018 USD ($)	Feb. 28, 2018 USD ($) Filings	Dec. 31, 2017 USD ($)	Nov. 30, 2017 USD ($)	Oct. 31, 2017 USD ($) MW	Sep. 30, 2017 USD ($) utility	Aug. 31, 2016 MW	Jun. 30, 2018 customer Assurance	Jun. 30, 2018 USD ($) customer change Assurance	Jun. 30, 2017
Regulatory environment
Corporate federal tax rate									21.00%	21.00%	35.00%
WE | Public Service Commission of Wisconsin (PSCW) | 2018 and 2019 rates
Regulatory environment
Approved return on equity (as a percent)							10.20%
Income Statement impact of flow through of repair related deferred tax liabilities | change										0
WE | Public Service Commission of Wisconsin (PSCW) | 2018 and 2019 rates | Electric rates
Regulatory environment
Percentage of current tax benefit from Tax Cuts and Jobs Act of 2017 to be used to reduce certain regulatory assets	80.00%
Percent of current tax benefit from Tax Cuts and Jobs Act of 2017 to be returned to customers via bill credits	20.00%
WE | Michigan Public Service Commission (MPSC)
Regulatory environment
Number of retail electric customers served in Michigan | customer									1	1
WG | Public Service Commission of Wisconsin (PSCW) | 2018 and 2019 rates
Regulatory environment
Approved return on equity (as a percent)							10.30%
WPS | Public Service Commission of Wisconsin (PSCW) | Badger Hollow and Two Creeks Solar Farms
Regulatory environment
Number of Solar Projects in WI that WPS Filed with the PSCW to Acquire an Interest In | solar_projects	2
WPS Ownership Interest in Badger Hollow and Two Creeks | MW	100
WPS Total Ownership Capacity in Badger Hollow and Two Creeks | MW	200
WPS Total Share of Cost of Badger Hollow and Two Creeks	$ 260.0
WPS | Public Service Commission of Wisconsin (PSCW) | 2018 and 2019 rates
Regulatory environment
Approved return on equity (as a percent)							10.00%
Authorized revenue requirement for the ReACT project							$ 275.0
AFUDC							51.0
Estimated cost of the ReACT project, excluding AFUDC							$ 342.0
WPS | Public Service Commission of Wisconsin (PSCW) | 2018 and 2019 rates | Electric rates
Regulatory environment
Percentage of current tax benefit from Tax Cuts and Jobs Act of 2017 to be used to reduce certain regulatory assets	40.00%
Percent of current tax benefit from Tax Cuts and Jobs Act of 2017 to be returned to customers via bill credits	60.00%
WE, WG, and WPS | Public Service Commission of Wisconsin (PSCW) | 2018 and 2019 rates
Regulatory environment
Number of utilities with earnings sharing mechanism | utility							3
Return on equity in excess of authorized amount (as a percent)							0.50%
Percentage of first 50 basis points of additional utility earnings shared with customers							50.00%
WE, WG, and WPS | Public Service Commission of Wisconsin (PSCW) | 2018 and 2019 rates | Natural gas rates
Regulatory environment
Percent of current tax benefit from Tax Cuts and Jobs Act of 2017 to be returned to customers via bill credits	100.00%
WE and WPS | Public Service Commission of Wisconsin (PSCW) | 2018 and 2019 rates | Electric rates
Regulatory environment
Decrease in Regulatory Assets Related to PSCW Tax Legislation Ruling										$ 46.9
PGL | Illinois Commerce Commission (ICC)
Regulatory environment
Amount of rate base reduction as a result of a settlement			$ 5.4
Amount to be refunded to ratepayers as a result of a settlement			$ 4.7
Amount of assurance that PGL's QIP rider costs will be recoverable | Assurance									0	0
MGU and UMERC | Michigan Public Service Commission (MPSC)
Regulatory environment
Number of filings required related to the Tax Cuts and Jobs Act of 2017 | Filings			3
MERC | Minnesota Public Utilities Commission (MPUC) | 2018 rates | Natural gas rates
Regulatory environment
Requested rate increase						$ 12.6
Requested rate increase (as a percent)						5.05%
Requested return on equity (as a percent)						10.30%
Requested common equity component average (as a percent)						50.90%
Interim rate increase		$ 7.0			$ 9.5
Interim rate increase, (as a percent)		2.81%			3.78%
Interim rate reduction		$ 2.5
Interim rates return on equity (as a percent)		9.10%
Interim rates common equity component average (as a percent)		50.90%
UMERC
Regulatory environment
Capacity of natural gas-fired generation facility (in megawatts) | MW						180
UMERC | Michigan Public Service Commission (MPSC)
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						$ 266.0
Estimated cost of constructing a power plant, including AFUDC						$ 277.0
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%
Utility Operations | Tax Cuts And Jobs Act Of 2017
Regulatory environment
Change in deferred taxes from tax legislation				$ 2,450.0