Regulatory Matters - Summary of Utilities Rate Plans (O&R New York-Electric) (Details) - USD ($)	1 Months Ended	12 Months Ended					36 Months Ended
	Jan. 31, 2024	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2024	Dec. 31, 2021
Public Utilities, General Disclosures [Line Items]
Deferred regulatory assets		$ 722,000,000	$ 702,000,000
Deferred regulatory liabilities		0	3,000,000	$ 7,000,000	$ 41,000,000			$ 7,000,000
O&R | Electric
Public Utilities, General Disclosures [Line Items]
Deferred regulatory assets					6,000,000	$ 100,000
Deferred regulatory liabilities		3,400,000	6,900,000	10,000,000				10,000,000
Negative revenue adjustments				0	0	0
Deferral of net increase (decrease) to regulatory assets		15,400,000	9,400,000	24,000,000	30,300,000	4,300,000
Deferred regulatory asset (liability)		$ 0	0	$ 0	(400,000)	$ 0		$ 0
Earnings sharing (percent)						9.60%
Common equity ratio (percent)								48.00%
Deferrals for property taxes limitation from rates (percent)								90.00%
Recovery of late payment charges, period (in years)		3 years
Recovery of late payment charges, amount		$ 2,200,000
Recovery of late payment charges, return on equity threshold rate		500.00%
O&R | Electric | Subsequent Event
Public Utilities, General Disclosures [Line Items]
Authorized return on common equity (percent)	10.25%
Common equity ratio (percent)	50.00%
Requested rate increase (decrease), amount	$ 18,100,000
O&R | Electric | Rate Plan for Year 1
Public Utilities, General Disclosures [Line Items]
Base rate changes								$ 13,400,000
Amortization to income of net regulatory assets								1,500,000
Potential earnings adjustment mechanism incentives								3,600,000
Potential incentive if target is met, related to service terminations								500,000
Weighted average cost of capital (after-tax)								$ 878,000,000
Weighted average cost of capital (after-tax) (percent)								6.97%
Authorized return on common equity (percent)								9.00%
Actual return on common equity (percent)								9.60%
Cost of long-term debt (percent)								5.17%
Requested rate increase (decrease), amount								$ 8,600,000
Regulatory assets, amortization period (in years)				6 years				6 years
Deferral, annual maximum (not more than) (percent)								0.10%
O&R | Electric | Rate Plan for Year 1 | Electric average excluding AMI
Public Utilities, General Disclosures [Line Items]
Average rate base								$ 1,008,000,000
O&R | Electric | Rate Plan for Year 1 | Advanced metering infrastructure (AMI)
Public Utilities, General Disclosures [Line Items]
Average rate base								48,000,000
O&R | Electric | Rate Plan for Year 1 | Maximum
Public Utilities, General Disclosures [Line Items]
Potential penalties (annually)								4,400,000
O&R | Electric | Rate Plan for Year 2
Public Utilities, General Disclosures [Line Items]
Base rate changes								8,000,000
Amortization to income of net regulatory assets								1,500,000
Potential earnings adjustment mechanism incentives								4,000,000
Potential incentive if target is met, related to service terminations								500,000
Weighted average cost of capital (after-tax)								$ 906,000,000
Weighted average cost of capital (after-tax) (percent)								6.96%
Actual return on common equity (percent)								8.76%
Cost of long-term debt (percent)								5.14%
Requested rate increase (decrease), amount								$ 12,100,000
Deferral, annual maximum (not more than) (percent)								0.075%
O&R | Electric | Rate Plan for Year 2 | Electric average excluding AMI
Public Utilities, General Disclosures [Line Items]
Average rate base								$ 1,032,000,000
O&R | Electric | Rate Plan for Year 2 | Advanced metering infrastructure (AMI)
Public Utilities, General Disclosures [Line Items]
Average rate base								58,000,000
O&R | Electric | Rate Plan for Year 2 | Maximum
Public Utilities, General Disclosures [Line Items]
Potential penalties (annually)								4,400,000
O&R | Electric | Rate Plan for Year 3
Public Utilities, General Disclosures [Line Items]
Base rate changes								5,800,000
Amortization to income of net regulatory assets								1,500,000
Potential earnings adjustment mechanism incentives								4,200,000
Potential incentive if target is met, related to service terminations		$ 1,500,000	$ 2,700,000					500,000
Weighted average cost of capital (after-tax)								$ 948,000,000
Weighted average cost of capital (after-tax) (percent)								6.96%
Actual return on common equity (percent)								9.16%
Cost of long-term debt (percent)								5.14%
Requested rate increase (decrease), amount								$ 12,200,000
Deferral, annual maximum (not more than) (percent)								0.05%
O&R | Electric | Rate Plan for Year 3 | Electric average excluding AMI
Public Utilities, General Disclosures [Line Items]
Average rate base								$ 1,083,000,000
O&R | Electric | Rate Plan for Year 3 | Advanced metering infrastructure (AMI)
Public Utilities, General Disclosures [Line Items]
Average rate base								61,000,000
O&R | Electric | Rate Plan for Year 3 | Maximum
Public Utilities, General Disclosures [Line Items]
Potential penalties (annually)								$ 4,500,000
O&R | Electric | Scenario, Forecast
Public Utilities, General Disclosures [Line Items]
Earnings sharing (percent)							9.70%
Common equity ratio (percent)							48.00%
O&R | Electric | Scenario, Forecast | Rate Plan for Year 1
Public Utilities, General Disclosures [Line Items]
Base rate changes							$ 4,900,000
Amortization to income of net regulatory assets							11,800,000
Potential earnings adjustment mechanism incentives							3,300,000
Weighted average cost of capital (after-tax)							$ 1,021,000,000
Weighted average cost of capital (after-tax) (percent)							6.77%
Authorized return on common equity (percent)							9.20%
Actual return on common equity (percent)							0.0009%
Cost of long-term debt (percent)							4.58%
Requested rate increase (decrease), amount							$ 11,700,000
Regulatory assets, amortization period (in years)							5 years
O&R | Electric | Scenario, Forecast | Rate Plan for Year 1 | Electric average excluding AMI
Public Utilities, General Disclosures [Line Items]
Average rate base							$ 1,175,000,000
O&R | Electric | Scenario, Forecast | Rate Plan for Year 1 | Maximum
Public Utilities, General Disclosures [Line Items]
Potential penalties (annually)							4,300,000
O&R | Electric | Scenario, Forecast | Rate Plan for Year 2
Public Utilities, General Disclosures [Line Items]
Base rate changes							16,200,000
Amortization to income of net regulatory assets							13,500,000
Potential earnings adjustment mechanism incentives							2,300,000
Weighted average cost of capital (after-tax)							$ 1,044,000,000
Weighted average cost of capital (after-tax) (percent)							6.73%
Actual return on common equity (percent)							0.00087%
Cost of long-term debt (percent)							4.51%
Requested rate increase (decrease), amount							$ 11,700,000
O&R | Electric | Scenario, Forecast | Rate Plan for Year 2 | Electric average excluding AMI
Public Utilities, General Disclosures [Line Items]
Average rate base							1,198,000,000
O&R | Electric | Scenario, Forecast | Rate Plan for Year 2 | Maximum
Public Utilities, General Disclosures [Line Items]
Potential penalties (annually)							4,400,000
O&R | Electric | Scenario, Forecast | Rate Plan for Year 3
Public Utilities, General Disclosures [Line Items]
Base rate changes							23,100,000
Amortization to income of net regulatory assets							15,200,000
Potential earnings adjustment mechanism incentives							4,000,000
Weighted average cost of capital (after-tax)							$ 1,144,000,000
Weighted average cost of capital (after-tax) (percent)							6.72%
Cost of long-term debt (percent)							4.49%
Requested rate increase (decrease), amount							$ 11,700,000
O&R | Electric | Scenario, Forecast | Rate Plan for Year 3 | Electric average excluding AMI
Public Utilities, General Disclosures [Line Items]
Average rate base							1,304,000,000
O&R | Electric | Scenario, Forecast | Rate Plan for Year 3 | Maximum
Public Utilities, General Disclosures [Line Items]
Potential penalties (annually)							$ 5,100,000
Energy Efficiency | O&R | Electric
Public Utilities, General Disclosures [Line Items]
Actual earnings adjustment mechanism incentives				$ 1,800,000	1,900,000	$ 2,600,000
Service Termination | O&R | Electric
Public Utilities, General Disclosures [Line Items]
Actual earnings adjustment mechanism incentives				0	$ 500,000	$ 200,000
Incentives reversed				$ 500,000