Industry Regulation - Rate Increases (Details) - USD ($) $ in Millions	Nov. 19, 2020	Jun. 15, 2016
NYSEG Electric | Year 1
Public Utility, Property, Plant and Equipment [Line Items]
Rate Increase	$ 34.0
Delivery Rate Increase	4.60%
NYSEG Electric | Year 2
Public Utility, Property, Plant and Equipment [Line Items]
Rate Increase	$ 46.0
Delivery Rate Increase	5.90%
NYSEG Electric | Year 3
Public Utility, Property, Plant and Equipment [Line Items]
Rate Increase	$ 36.0	$ 30.0
Delivery Rate Increase	4.20%	4.10%
NYSEG Gas | Year 1
Public Utility, Property, Plant and Equipment [Line Items]
Rate Increase	$ 0.0
Delivery Rate Increase	0.00%
NYSEG Gas | Year 2
Public Utility, Property, Plant and Equipment [Line Items]
Rate Increase	$ 2.0
Delivery Rate Increase	0.80%
NYSEG Gas | Year 3
Public Utility, Property, Plant and Equipment [Line Items]
Rate Increase	$ 3.0	$ 15.0
Delivery Rate Increase	1.60%	7.30%
RG&E Electric | Year 1
Public Utility, Property, Plant and Equipment [Line Items]
Rate Increase	$ 17.0
Delivery Rate Increase	3.80%
RG&E Electric | Year 2
Public Utility, Property, Plant and Equipment [Line Items]
Rate Increase	$ 14.0
Delivery Rate Increase	3.20%
RG&E Electric | Year 3
Public Utility, Property, Plant and Equipment [Line Items]
Rate Increase	$ 16.0	$ 26.0
Delivery Rate Increase	3.30%	5.70%
RG&E Gas | Year 1
Public Utility, Property, Plant and Equipment [Line Items]
Rate Increase	$ 0.0
Delivery Rate Increase	0.00%
RG&E Gas | Year 2
Public Utility, Property, Plant and Equipment [Line Items]
Rate Increase	$ 0.0
Delivery Rate Increase	0.00%
RG&E Gas | Year 3
Public Utility, Property, Plant and Equipment [Line Items]
Rate Increase	$ 2.0	$ 10.0
Delivery Rate Increase	1.30%	5.20%