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PROPERTY, PLANT AND EQUIPMENT AND ACCUMULATED DEPRECIATION
 12 Months Ended
Dec. 31, 2020
Property, Plant and Equipment [Abstract]  
PROPERTY, PLANT AND EQUIPMENT AND ACCUMULATED DEPRECIATION PROPERTY, PLANT AND EQUIPMENT AND ACCUMULATED DEPRECIATION
Utility property, plant and equipment is recorded at original cost.  Original cost includes materials, labor, construction overheads and AFUDC for regulated property.  The cost of repairs and maintenance is charged to Operations and Maintenance expense as incurred.  

The following tables summarize property, plant and equipment by asset category:
EversourceAs of December 31,
(Millions of Dollars)20202019
Distribution - Electric$16,703.2 $15,880.0 
Distribution - Natural Gas6,111.2 3,931.1 
Transmission - Electric11,954.0 10,958.4 
Distribution - Water1,743.1 1,726.5 
Solar201.5 200.2 
Utility36,713.0 32,696.2 
Other (1)
1,269.0 1,025.6 
Property, Plant and Equipment, Gross37,982.0 33,721.8 
Less:  Accumulated Depreciation  
Utility    (8,476.3)(7,483.5)
Other(477.6)(387.4)
Total Accumulated Depreciation(8,953.9)(7,870.9)
Property, Plant and Equipment, Net29,028.1 25,850.9 
Construction Work in Progress1,854.4 1,734.6 
Total Property, Plant and Equipment, Net$30,882.5 $27,585.5 
 As of December 31,
 20202019
(Millions of Dollars)CL&PNSTAR
Electric		PSNHCL&PNSTAR
Electric		PSNH
Distribution - Electric$6,820.7 $7,544.4 $2,378.4 $6,485.5 $7,163.7 $2,271.1 
Transmission - Electric5,512.0 4,701.3 1,742.4 5,043.0 4,411.9 1,498.7 
Solar— 201.5 — — 200.2 — 
Property, Plant and Equipment, Gross12,332.7 12,447.2 4,120.8 11,528.5 11,775.8 3,769.8 
Less:  Accumulated Depreciation(2,475.4)(3,074.1)(848.9)(2,385.7)(2,895.3)(799.9)
Property, Plant and Equipment, Net9,857.3 9,373.1 3,271.9 9,142.8 8,880.5 2,969.9 
Construction Work in Progress377.3 750.0 102.4 483.0 592.3 159.6 
Total Property, Plant and Equipment, Net$10,234.6 $10,123.1 $3,374.3 $9,625.8 $9,472.8 $3,129.5 

(1)These assets are primarily comprised of computer software, hardware and equipment at Eversource Service and buildings at The Rocky River Realty Company.

On October 9, 2020, Eversource completed the CMA asset acquisition. EGMA’s net plant assets of $1.20 billion are reflected in the natural gas distribution asset category as of December 31, 2020.

On July 31, 2020, Eversource sold its water system and treatment plant that supplies water to the towns of Hingham, Hull and North Cohasset to the town of Hingham, Massachusetts. Net property, plant and equipment of $63.9 million and goodwill of $23.6 million were included in determining the gain on sale. Proceeds from the sale were $110.5 million, with a pre-tax gain of $16.0 million (after-tax gain of $3.5 million) recognized within Operations and Maintenance Expense on the statement of income for the year ended December 31, 2020. The assets and liabilities associated with the sale of the business were previously reflected in the Water Distribution segment and reporting unit.

Depreciation: Depreciation of utility assets is calculated on a straight-line basis using composite rates based on the estimated remaining useful lives of the various classes of property (estimated useful life for PSNH distribution and the water utilities).  The composite rates, which are subject to approval by the appropriate state regulatory agency, include a cost of removal component, which is collected from customers over the lives of the plant assets and is recognized as a regulatory liability.  Depreciation rates are applied to property from the time it is placed in service.

Upon retirement from service, the cost of the utility asset is charged to the accumulated provision for depreciation.  The actual incurred removal costs are applied against the related regulatory liability.  
The depreciation rates for the various classes of utility property, plant and equipment aggregate to composite rates as follows:
(Percent)202020192018
Eversource3.0 %3.0 %2.9 %
CL&P2.8 %2.8 %2.8 %
NSTAR Electric2.8 %2.8 %2.8 %
PSNH2.8 %2.8 %2.8 %

The following table summarizes average remaining useful lives of depreciable assets:
 As of December 31, 2020
(Years)EversourceCL&PNSTAR ElectricPSNH
Distribution - Electric34.335.433.733.3
Distribution - Natural Gas41.5— — — 
Transmission - Electric40.736.945.542.6
Distribution - Water34.1— — — 
Solar24.3— 24.3— 
Other (1)
11.0— — — 

(1)The estimated useful life of computer software, hardware and equipment primarily ranges from 5 to 15 years and of buildings is 40 years.