REGULATORY ENVIRONMENT - NSG 2021 RATE CASE (Details) - Illinois Commerce Commission (ICC) - NSG $ in Millions	Sep. 08, 2021 USD ($)
Public Utilities, General Disclosures [Line Items]
Approved rate increase	$ 4.1
Approved rate increase (as a percent)	4.50%
Approved return on equity (as a percent)	9.67%
Approved common equity component average (as a percent)	51.58%