Regulatory Matters - Summary of Utilities Rate Plans (O&R New York-Electric) (Details) - USD ($) $ in Millions	1 Months Ended	12 Months Ended						36 Months Ended
	Jan. 31, 2024	Dec. 31, 2028	Dec. 31, 2027	Dec. 31, 2026	Dec. 31, 2024	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2027	Dec. 31, 2024	Dec. 31, 2021
Public Utilities, General Disclosures [Line Items]
Deferred regulatory assets					$ 848.0	$ 722.0			$ 848.0
Deferred regulatory liabilities					$ 0.0	0.0	$ 3.0		$ 0.0	$ 7.0
O&R | Electric
Public Utilities, General Disclosures [Line Items]
Deferred regulatory assets						3.4	6.9
Deferral of net increase (decrease) to regulatory assets						15.4	9.4
Authorized return on common equity (percent)	10.10%
Earnings sharing (percent)					9.70%				9.70%
Common equity ratio (percent)	48.00%								48.00%
Recovery of late payment charges, period (in years)					3 years
Recovery of late payment charges, amount					$ 2.2
Recovery of late payment charges, return on equity threshold rate					500.00%
Regulatory assets usefull life					15 years
Uncollecetible expenses, threshold amount					$ 0.9
Surcharge recovery threshold percentage					50.00%
O&R | Electric | Rate Plan for Year 1
Public Utilities, General Disclosures [Line Items]
Base rate changes									$ 4.9
Amortization to income of net regulatory assets									11.8
Potential earnings adjustment mechanism incentives									3.3
Weighted average cost of capital (after-tax)									$ 1,021.0
Weighted average cost of capital (after-tax) (percent)									6.77%
Authorized return on common equity (percent)									9.20%
Actual return on common equity (percent)									8.96%
Cost of long-term debt (percent)									4.58%
Requested rate increase (decrease), amount									$ 11.7
Regulatory assets, amortization period (in years)					5 years				5 years
Deferral, annual maximum (not more than) (percent)									1000.00%
O&R | Electric | Rate Plan for Year 1 | Electric average excluding AMI
Public Utilities, General Disclosures [Line Items]
Average rate base									$ 1,175.0
O&R | Electric | Rate Plan for Year 1 | Maximum
Public Utilities, General Disclosures [Line Items]
Potential penalties (annually)									4.3
O&R | Electric | Rate Plan for Year 2
Public Utilities, General Disclosures [Line Items]
Base rate changes									16.2
Amortization to income of net regulatory assets									13.5
Potential earnings adjustment mechanism incentives									2.3
Weighted average cost of capital (after-tax)									$ 1,044.0
Weighted average cost of capital (after-tax) (percent)									6.73%
Actual return on common equity (percent)									8.73%
Cost of long-term debt (percent)									4.51%
Requested rate increase (decrease), amount									$ 11.7
Deferral, annual maximum (not more than) (percent)									750.00%
O&R | Electric | Rate Plan for Year 2 | Electric average excluding AMI
Public Utilities, General Disclosures [Line Items]
Average rate base									$ 1,198.0
O&R | Electric | Rate Plan for Year 2 | Maximum
Public Utilities, General Disclosures [Line Items]
Potential penalties (annually)									4.4
O&R | Electric | Rate Plan for Year 3
Public Utilities, General Disclosures [Line Items]
Base rate changes									23.1
Amortization to income of net regulatory assets									15.2
Potential earnings adjustment mechanism incentives									4.0
Potential incentive if target is met, related to service terminations						1.5	$ 2.7
Weighted average cost of capital (after-tax)									$ 1,144.0
Weighted average cost of capital (after-tax) (percent)									6.72%
Actual return on common equity (percent)									9.86%
Cost of long-term debt (percent)									4.49%
Requested rate increase (decrease), amount									$ 11.7
Deferral, annual maximum (not more than) (percent)									500.00%
O&R | Electric | Rate Plan for Year 3 | Electric average excluding AMI
Public Utilities, General Disclosures [Line Items]
Average rate base									$ 1,304.0
O&R | Electric | Rate Plan for Year 3 | Maximum
Public Utilities, General Disclosures [Line Items]
Potential penalties (annually)									5.1
O&R | Electric | Scenario, Forecast
Public Utilities, General Disclosures [Line Items]
Earnings sharing (percent)			10.25%					10.25%
Common equity ratio (percent)								48.00%
Requested rate increase (decrease), amount		$ 880.0	$ 932.0
O&R | Electric | Scenario, Forecast | Rate Plan for Year 1
Public Utilities, General Disclosures [Line Items]
Base rate changes								$ (13.1)
Amortization to income of net regulatory assets								4.5
Potential earnings adjustment mechanism incentives								3.9
Weighted average cost of capital (after-tax)								$ 1,293.0
Weighted average cost of capital (after-tax) (percent)								7.25%
Authorized return on common equity (percent)								9.75%
Cost of long-term debt (percent)								4.95%
O&R | Electric | Scenario, Forecast | Rate Plan for Year 1 | Electric average excluding AMI
Public Utilities, General Disclosures [Line Items]
Average rate base								$ 1,398.0
O&R | Electric | Scenario, Forecast | Rate Plan for Year 1 | Maximum
Public Utilities, General Disclosures [Line Items]
Potential penalties (annually)								7.6
O&R | Electric | Scenario, Forecast | Rate Plan for Year 2
Public Utilities, General Disclosures [Line Items]
Base rate changes								24.8
Amortization to income of net regulatory assets								5.4
Potential earnings adjustment mechanism incentives								4.7
Weighted average cost of capital (after-tax)								$ 1,393.0
Weighted average cost of capital (after-tax) (percent)								7.28%
Cost of long-term debt (percent)								5.01%
O&R | Electric | Scenario, Forecast | Rate Plan for Year 2 | Electric average excluding AMI
Public Utilities, General Disclosures [Line Items]
Average rate base								$ 1,471.0
O&R | Electric | Scenario, Forecast | Rate Plan for Year 2 | Maximum
Public Utilities, General Disclosures [Line Items]
Potential penalties (annually)								8.5
O&R | Electric | Scenario, Forecast | Rate Plan for Year 3
Public Utilities, General Disclosures [Line Items]
Base rate changes								44.1
Amortization to income of net regulatory assets								6.4
Potential earnings adjustment mechanism incentives								5.8
Weighted average cost of capital (after-tax)								$ 1,646.0
Weighted average cost of capital (after-tax) (percent)								7.31%
Cost of long-term debt (percent)								5.08%
O&R | Electric | Scenario, Forecast | Rate Plan for Year 3 | Electric average excluding AMI
Public Utilities, General Disclosures [Line Items]
Average rate base								$ 1,737.0
O&R | Electric | Scenario, Forecast | Rate Plan for Year 3 | Maximum
Public Utilities, General Disclosures [Line Items]
Potential penalties (annually)								$ 11.5
O&R | Gas
Public Utilities, General Disclosures [Line Items]
Deferred regulatory assets					$ 2.0	$ 7.6			$ 2.0
Deferrals for property taxes limitation from rates (percent)									90.00%
Recovery of late payment charges, amount					$ 0.6
Regulatory assets usefull life					15 years
Uncollecetible expenses, threshold amount					$ 0.5
Surcharge recovery threshold percentage					50.00%
O&R | Gas | Rate Plan for Year 1
Public Utilities, General Disclosures [Line Items]
Base rate changes									$ 0.7
Amortization to income of net regulatory assets									0.8
Potential earnings adjustment mechanism incentives									$ 0.2
Authorized return on common equity (percent)					9.20%
Requested rate increase (decrease), amount										4.4
Deferral, annual maximum (not more than) (percent)									0.10%
O&R | Gas | Rate Plan for Year 2
Public Utilities, General Disclosures [Line Items]
Base rate changes									$ 7.4
Amortization to income of net regulatory assets									0.7
Potential earnings adjustment mechanism incentives									$ 0.2
Requested rate increase (decrease), amount										4.4
Deferral, annual maximum (not more than) (percent)									0.075%
O&R | Gas | Rate Plan for Year 3
Public Utilities, General Disclosures [Line Items]
Base rate changes									$ 9.9
Amortization to income of net regulatory assets									0.3
Potential earnings adjustment mechanism incentives									$ 0.4
Requested rate increase (decrease), amount										$ 4.4
Deferral, annual maximum (not more than) (percent)									0.05%
O&R | Gas | Scenario, Forecast
Public Utilities, General Disclosures [Line Items]
Authorized return on common equity (percent)			10.10%	10.10%
Common equity ratio (percent)		48.00%	48.00%	48.00%				48.00%
Requested rate increase (decrease), amount		$ 166.0	$ 266.0	$ 441.0
O&R | Gas | Scenario, Forecast | Rate Plan for Year 1
Public Utilities, General Disclosures [Line Items]
Base rate changes								$ 3.6
Amortization to income of net regulatory assets								$ 8.4
Authorized return on common equity (percent)								9.75%
O&R | Gas | Scenario, Forecast | Rate Plan for Year 2
Public Utilities, General Disclosures [Line Items]
Base rate changes								$ 18.0
Amortization to income of net regulatory assets								8.2
O&R | Gas | Scenario, Forecast | Rate Plan for Year 3
Public Utilities, General Disclosures [Line Items]
Base rate changes								16.5
Amortization to income of net regulatory assets								$ 8.0