REGULATORY ENVIRONMENT - WI 2020 AND 2021 RATES (Details) - Public Service Commission of Wisconsin (PSCW) $ in Millions	1 Months Ended
	Dec. 31, 2019 USD ($) utility	Sep. 30, 2017 USD ($)
2020 and 2021 rates
Public Utilities, General Disclosures [Line Items]
Number of utilities filing rate requests | utility	3
Number of utilities with earnings sharing mechanism | utility	3
Percentage of first 25 basis points of additional earnings retained by the utility	100.00%
Return on equity in excess of authorized amount (as a percent)	0.25%
Percentage of additional earnings between 25 and 75 basis points refunded to customers	50.00%
Return on equity in excess of first 25 basis points above authorized amount (as a percent)	0.50%
Percentage of earnings in excess of 75 basis points refunded to customers	100.00%
Electric rates | 2020 and 2021 rates | Tax Cuts and Jobs Act of 2017
Public Utilities, General Disclosures [Line Items]
Amortization period	2 years
Natural gas rates | 2020 and 2021 rates | Tax Cuts and Jobs Act of 2017
Public Utilities, General Disclosures [Line Items]
Number of utilities filing rate requests | utility	3
Amortization period	4 years
WE | 2020 and 2021 rates
Public Utilities, General Disclosures [Line Items]
Approved return on equity (as a percent)	10.00%
Approved common equity component average (as a percent)	52.50%
WE | Electric rates | 2020 rates
Public Utilities, General Disclosures [Line Items]
Approved rate increase	$ 15.3
Approved rate increase (as a percent)	0.50%
WE | Electric rates | 2020 rates | Tax Cuts and Jobs Act of 2017
Public Utilities, General Disclosures [Line Items]
Amortization of regulatory liabilities	$ 65.0
WE | Electric rates | 2021 rates | Tax Cuts and Jobs Act of 2017
Public Utilities, General Disclosures [Line Items]
Amortization of regulatory liabilities	65.0
WE | Electric rates | 2020 and 2021 rates
Public Utilities, General Disclosures [Line Items]
Pleasant Prairie power plant's book value to be securitized	100.0
WE | Natural gas rates | 2020 rates
Public Utilities, General Disclosures [Line Items]
Approved rate increase	$ 10.4
Approved rate increase (as a percent)	2.80%
WE | Natural gas rates | 2020 rates | Tax Cuts and Jobs Act of 2017
Public Utilities, General Disclosures [Line Items]
Amortization of regulatory liabilities	$ (5.0)
WE | Natural gas rates | 2021 rates | Tax Cuts and Jobs Act of 2017
Public Utilities, General Disclosures [Line Items]
Amortization of regulatory liabilities	(5.0)
WE | Steam rates | 2020 rates
Public Utilities, General Disclosures [Line Items]
Approved rate increase	$ 1.9
Approved rate increase (as a percent)	8.60%
WPS | 2020 and 2021 rates
Public Utilities, General Disclosures [Line Items]
Approved return on equity (as a percent)	10.00%
Approved common equity component average (as a percent)	52.50%
WPS | Electric rates | 2020 rates
Public Utilities, General Disclosures [Line Items]
Approved rate increase	$ 15.8
Approved rate increase (as a percent)	1.60%
WPS | Electric rates | 2020 rates | Tax Cuts and Jobs Act of 2017
Public Utilities, General Disclosures [Line Items]
Amortization of regulatory liabilities	$ 11.0
WPS | Electric rates | 2021 rates | Tax Cuts and Jobs Act of 2017
Public Utilities, General Disclosures [Line Items]
Amortization of regulatory liabilities	39.0
WPS | Electric rates | 2020 and 2021 rates
Public Utilities, General Disclosures [Line Items]
Authorized revenue requirement for ReACT		$ 275.0
Cost of the ReACT project	$ 342.0
WPS | Electric rates | 2020 and 2021 rates | ReACT
Public Utilities, General Disclosures [Line Items]
Collection of ReACT regulatory asset in years	8 years
WPS | Electric rates | 2020 and 2021 rates | Earnings sharing mechanisms
Public Utilities, General Disclosures [Line Items]
Amortization period	2 years
Amortization of regulatory liabilities	$ 21.0
WPS | Natural gas rates | 2020 rates
Public Utilities, General Disclosures [Line Items]
Approved rate increase	$ 4.3
Approved rate increase (as a percent)	1.40%
WPS | Natural gas rates | 2020 rates | Tax Cuts and Jobs Act of 2017
Public Utilities, General Disclosures [Line Items]
Amortization of regulatory liabilities	$ 5.0
WPS | Natural gas rates | 2021 rates | Tax Cuts and Jobs Act of 2017
Public Utilities, General Disclosures [Line Items]
Amortization of regulatory liabilities	$ 5.0
WG | 2020 and 2021 rates
Public Utilities, General Disclosures [Line Items]
Approved return on equity (as a percent)	10.20%
Approved common equity component average (as a percent)	52.50%
WG | Natural gas rates | 2020 rates
Public Utilities, General Disclosures [Line Items]
Approved rate increase	$ (1.5)
Approved rate increase (as a percent)	(0.20%)
WG | Natural gas rates | 2020 rates | Tax Cuts and Jobs Act of 2017
Public Utilities, General Disclosures [Line Items]
Amortization of regulatory liabilities	$ 3.0
WG | Natural gas rates | 2021 rates | Tax Cuts and Jobs Act of 2017
Public Utilities, General Disclosures [Line Items]
Amortization of regulatory liabilities	$ 3.0