LEASES - Future Minimum Lease Payments under Long-Term Leases (Details) $ in Millions	Sep. 30, 2019 USD ($)
Operating Leases
October 1, 2019 through December 31, 2019	$ 2.6
Year Ending December 31,
2020	10.1
2021	8.9
2022	7.4
2023	4.9
2024	2.8
Thereafter	28.9
Future lease payments	65.6
Less amount representing interest	13.3
Present value of future minimum lease payments	52.3
Finance Leases
October 1, 2019 through December 31, 2019	0.9
Year Ending December 31,
2020	3.4
2021	2.9
2022	1.5
2023	0.7
2024	0.7
Thereafter	13.3
Future lease payments	23.4
Less amount representing interest	12.4
Present value of future minimum lease payments	11.0
CL&P
Operating Leases
October 1, 2019 through December 31, 2019	0.1
Year Ending December 31,
2020	0.5
2021	0.2
2022	0.0
2023	0.0
2024	0.0
Thereafter	0.1
Future lease payments	0.9
Less amount representing interest	0.0
Present value of future minimum lease payments	0.9
Finance Leases
October 1, 2019 through December 31, 2019	0.5
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	4.0
Less amount representing interest	0.6
Present value of future minimum lease payments	3.4
NSTAR Electric
Operating Leases
October 1, 2019 through December 31, 2019	0.3
Year Ending December 31,
2020	1.6
2021	1.6
2022	1.6
2023	1.6
2024	1.6
Thereafter	28.7
Future lease payments	37.0
Less amount representing interest	12.8
Present value of future minimum lease payments	24.2
Finance Leases
October 1, 2019 through December 31, 2019	0.1
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	15.7
Less amount representing interest	11.3
Present value of future minimum lease payments	4.4
PSNH
Operating Leases
October 1, 2019 through December 31, 2019	0.0
Year Ending December 31,
2020	0.1
2021	0.1
2022	0.1
2023	0.0
2024	0.0
Thereafter	0.2
Future lease payments	0.5
Less amount representing interest	0.1
Present value of future minimum lease payments	0.4
Finance Leases
October 1, 2019 through December 31, 2019	0.0
Year Ending December 31,
2020	0.1
2021	0.1
2022	0.1
2023	0.1
2024	0.1
Thereafter	0.5
Future lease payments	1.0
Less amount representing interest	0.1
Present value of future minimum lease payments	$ 0.9