LEASES - Future Minimum Lease Payments under Long-Term Leases (Details) - USD ($) $ in Millions	Dec. 31, 2023	Dec. 31, 2022
Operating Leases
2024	$ 11.1
2025	8.3
2026	6.9
2027	4.3
2028	4.3
Thereafter	30.3
Future lease payments	65.2
Less amount representing interest	11.7
Present value of future minimum lease payments	53.5	$ 56.9
Finance Leases
2024	7.8
2025	8.2
2026	7.8
2027	7.9
2028	7.2
Thereafter	57.8
Future lease payments	96.7
Less amount representing interest	24.0
Present value of future minimum lease payments	72.7	58.0
CL&P
Operating Leases
2024	0.9
2025	0.9
2026	0.5
2027	0.0
2028	0.0
Thereafter	0.0
Future lease payments	2.3
Less amount representing interest	0.1
Present value of future minimum lease payments	2.2	2.2
Finance Leases
2024	1.9
2025	2.3
2026	2.4
2027	2.5
2028	2.6
Thereafter	11.5
Future lease payments	23.2
Less amount representing interest	4.9
Present value of future minimum lease payments	18.3	0.0
NSTAR Electric
Operating Leases
2024	3.4
2025	3.0
2026	3.0
2027	2.3
2028	2.4
Thereafter	24.6
Future lease payments	38.7
Less amount representing interest	11.0
Present value of future minimum lease payments	27.7	22.5
Finance Leases
2024	0.6
2025	0.7
2026	0.7
2027	0.7
2028	0.7
Thereafter	11.0
Future lease payments	14.4
Less amount representing interest	9.5
Present value of future minimum lease payments	4.9	4.9
PSNH
Operating Leases
2024	1.7
2025	1.7
2026	1.5
2027	0.1
2028	0.0
Thereafter	0.0
Future lease payments	5.0
Less amount representing interest	0.3
Present value of future minimum lease payments	4.7	0.0
Finance Leases
Present value of future minimum lease payments	$ 0.0	$ 0.0