REGULATORY ENVIRONMENT - NSG 2021 RATE CASE (Details) - Illinois Commerce Commission (ICC) - NSG $ in Millions	Oct. 15, 2020 USD ($)
Public Utilities, General Disclosures [Line Items]
Requested rate increase	$ 7.6
Requested rate increase (as a percent)	8.50%
Requested return on equity (as a percent)	10.00%
Requested common equity component average (as a percent)	52.50%