Regulatory Environment - PGL (Details) - Illinois Commerce Commission (ICC) - PGL $ in Millions	Dec. 31, 2020 Assurance	Jul. 31, 2019 USD ($)	Feb. 01, 2018 USD ($)
Public Utilities, General Disclosures [Line Items]
Rate base reduction from settlement of reconciliation		$ 7.0	$ 5.4
Total refunds required to ratepayers from settlement		$ 7.3	$ 4.7
Amount of assurance that PGL's QIP rider costs will be recoverable | Assurance	0