REGULATORY ENVIRONMENT - RECOVERY OF NATURAL GAS COSTS (Details) - USD ($)		1 Months Ended
	Mar. 30, 2021	Feb. 28, 2021	Mar. 31, 2021	Dec. 31, 2020
Public Utilities, General Disclosures [Line Items]
Amounts recoverable from customers			$ 306,700,000	$ 20,000,000.0
Public Service Commission of Wisconsin (PSCW) | Excess Natural Gas Costs
Public Utilities, General Disclosures [Line Items]
Recovery period of regulatory asset	3 months
Illinois Commerce Commission (ICC) | Excess Natural Gas Costs
Public Utilities, General Disclosures [Line Items]
Recovery period of regulatory asset		12 months
WE | Public Service Commission of Wisconsin (PSCW) | Excess Natural Gas Costs
Public Utilities, General Disclosures [Line Items]
Amounts recoverable from customers	$ 54,000,000
WG | Public Service Commission of Wisconsin (PSCW) | Excess Natural Gas Costs
Public Utilities, General Disclosures [Line Items]
Amounts recoverable from customers	24,000,000
WPS | Public Service Commission of Wisconsin (PSCW) | Excess Natural Gas Costs
Public Utilities, General Disclosures [Line Items]
Amounts recoverable from customers	$ 28,000,000
Recovery period of regulatory asset	3 months
PGL | Illinois Commerce Commission (ICC) | Excess Natural Gas Costs
Public Utilities, General Disclosures [Line Items]
Amounts recoverable from customers		$ 131,000,000
NSG | Illinois Commerce Commission (ICC) | Excess Natural Gas Costs
Public Utilities, General Disclosures [Line Items]
Amounts recoverable from customers		10,000,000
MERC | Minnesota Public Utilities Commission (MPUC) | Excess Natural Gas Costs
Public Utilities, General Disclosures [Line Items]
Amounts recoverable from customers		$ 75,000,000
Recovery period of regulatory asset		12 months