Regulatory Assets and Liabilities - Rate Increases and Delivery Rate Percentages (Details) $ in Millions	Jun. 22, 2020 USD ($)
NYSEG Electric | Electric and Gas Service Rate Plan Year One
Regulatory Liabilities [Line Items]
Rate Increase	$ 34
Delivery rate increase	4.60%
NYSEG Electric | Electric and Gas Service Rate Plan Year Two
Regulatory Liabilities [Line Items]
Rate Increase	$ 46
Delivery rate increase	5.90%
NYSEG Electric | Electric and Gas Service Rate Plan Year Three
Regulatory Liabilities [Line Items]
Rate Increase	$ 36
Delivery rate increase	4.20%
NYSEG Gas | Electric and Gas Service Rate Plan Year One
Regulatory Liabilities [Line Items]
Rate Increase	$ 0
Delivery rate increase	0.00%
NYSEG Gas | Electric and Gas Service Rate Plan Year Two
Regulatory Liabilities [Line Items]
Rate Increase	$ 2
Delivery rate increase	0.80%
NYSEG Gas | Electric and Gas Service Rate Plan Year Three
Regulatory Liabilities [Line Items]
Rate Increase	$ 3
Delivery rate increase	1.60%
RG&E Electric | Electric and Gas Service Rate Plan Year One
Regulatory Liabilities [Line Items]
Rate Increase	$ 17
Delivery rate increase	3.80%
RG&E Electric | Electric and Gas Service Rate Plan Year Two
Regulatory Liabilities [Line Items]
Rate Increase	$ 14
Delivery rate increase	3.20%
RG&E Electric | Electric and Gas Service Rate Plan Year Three
Regulatory Liabilities [Line Items]
Rate Increase	$ 16
Delivery rate increase	3.30%
RG&E Gas | Electric and Gas Service Rate Plan Year One
Regulatory Liabilities [Line Items]
Rate Increase	$ 0
Delivery rate increase	0.00%
RG&E Gas | Electric and Gas Service Rate Plan Year Two
Regulatory Liabilities [Line Items]
Rate Increase	$ 0
Delivery rate increase	0.00%
RG&E Gas | Electric and Gas Service Rate Plan Year Three
Regulatory Liabilities [Line Items]
Rate Increase	$ 2
Delivery rate increase	1.30%