LEASES - Future Minimum Lease Payments under Long-Term Leases (Details) $ in Millions	Jun. 30, 2019 USD ($)
Operating Leases
July 1, 2019 through December 31, 2019	$ 5.7
Year Ending December 31,
2020	10.3
2021	9.2
2022	7.5
2023	4.9
2024	2.9
Thereafter	29.2
Future lease payments	69.7
Less amount representing interest	15.1
Present value of future minimum lease payments	54.6
Finance Leases
July 1, 2019 through December 31, 2019	1.7
Year Ending December 31,
2020	3.4
2021	2.9
2022	1.5
2023	0.7
2024	0.7
Thereafter	13.2
Future lease payments	24.1
Less amount representing interest	12.5
Present value of future minimum lease payments	11.6
CL&P
Operating Leases
July 1, 2019 through December 31, 2019	0.3
Year Ending December 31,
2020	0.2
2021	0.1
2022	0.0
2023	0.0
2024	0.0
Thereafter	0.1
Future lease payments	0.7
Less amount representing interest	0.1
Present value of future minimum lease payments	0.6
Finance Leases
July 1, 2019 through December 31, 2019	1.0
Year Ending December 31,
2020	2.0
2021	1.5
2022	0.0
2023	0.0
2024	0.0
Thereafter	0.0
Future lease payments	4.5
Less amount representing interest	0.7
Present value of future minimum lease payments	3.8
NSTAR Electric
Operating Leases
July 1, 2019 through December 31, 2019	0.8
Year Ending December 31,
2020	1.6
2021	1.6
2022	1.6
2023	1.6
2024	1.7
Thereafter	28.9
Future lease payments	37.8
Less amount representing interest	13.4
Present value of future minimum lease payments	24.4
Finance Leases
July 1, 2019 through December 31, 2019	0.3
Year Ending December 31,
2020	0.5
2021	0.5
2022	0.6
2023	0.6
2024	0.6
Thereafter	12.8
Future lease payments	15.9
Less amount representing interest	11.5
Present value of future minimum lease payments	4.4
PSNH
Operating Leases
July 1, 2019 through December 31, 2019	0.2
Year Ending December 31,
2020	0.2
2021	0.2
2022	0.1
2023	0.1
2024	0.0
Thereafter	0.2
Future lease payments	1.0
Less amount representing interest	0.2
Present value of future minimum lease payments	0.8
Finance Leases
July 1, 2019 through December 31, 2019	0.1
Year Ending December 31,
2020	0.1
2021	0.1
2022	0.1
2023	0.1
2024	0.1
Thereafter	0.4
Future lease payments	1.0
Less amount representing interest	0.1
Present value of future minimum lease payments	$ 0.9