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PROPERTY, PLANT AND EQUIPMENT AND ACCUMULATED DEPRECIATION (Tables)
 12 Months Ended
Dec. 31, 2017
Property, Plant and Equipment [Abstract]  
Schedule of Utility Property, Plant and Equipment
The following tables summarize property, plant and equipment by asset category:
Eversource
As of December 31,
(Millions of Dollars)
2017
 
2016
Distribution - Electric
$
14,410.5

 
$
13,716.9

Distribution - Natural Gas
3,244.2

 
3,010.4

Transmission - Electric
9,270.9

 
8,517.4

Water (1)
1,558.4

 
—

Generation and Solar(2)
36.2

 
1,224.2

Utility
28,520.2

 
26,468.9

Other (3)
693.7

 
591.6

Property, Plant and Equipment, Gross
29,213.9

 
27,060.5

Less:  Accumulated Depreciation
 
 
 
Utility    
(6,846.9
)
 
(6,480.4
)
Other
(286.9
)
 
(242.0
)
Total Accumulated Depreciation
(7,133.8
)
 
(6,722.4
)
Property, Plant and Equipment, Net
22,080.1

 
20,338.1

Construction Work in Progress
1,537.4

 
1,012.4

Total Property, Plant and Equipment, Net
$
23,617.5

 
$
21,350.5

 
As of December 31,
 
2017
 
2016
(Millions of Dollars)
CL&P
 
NSTAR
Electric
 
PSNH
 
CL&P
 
NSTAR
Electric
 
PSNH
Distribution
$
5,888.3

 
$
6,479.0

 
$
2,083.4

 
$
5,562.9

 
$
6,244.2

 
$
1,949.8

Transmission
4,239.9

 
3,821.2

 
1,161.3

 
3,912.9

 
3,496.9

 
1,059.3

Generation and Solar (2)
—

 
36.2

 
—

 
—

 
36.0

 
1,188.2

Property, Plant and Equipment, Gross
10,128.2

 
10,336.4

 
3,244.7

 
9,475.8

 
9,777.1

 
4,197.3

Less:  Accumulated Depreciation
(2,239.0
)
 
(2,550.2
)
 
(751.8
)
 
(2,082.4
)
 
(2,364.2
)
 
(1,254.7
)
Property, Plant and Equipment, Net
7,889.2

 
7,786.2

 
2,492.9

 
7,393.4

 
7,412.9

 
2,942.6

Construction Work in Progress
381.8

 
460.3

 
149.4

 
239.0

 
317.2

 
96.7

Total Property, Plant and Equipment, Net
$
8,271.0

 
$
8,246.5

 
$
2,642.3

 
$
7,632.4

 
$
7,730.1

 
$
3,039.3


(1) 
On December 4, 2017, Eversource completed the acquisition of Aquarion. See Note 22A, "Acquisition of Aquarion and Goodwill - Acquisition of Aquarion," for further information.

(2) 
On October 11, 2017, PSNH entered into two Purchase and Sale Agreements ("Agreements") to sell its thermal and hydroelectric generation assets. As of December 31, 2017, PSNH has classified its generation assets as held for sale. As of December 31, 2016, these plant balances were recorded within Property, Plant and Equipment, Net on the balance sheet. See Note 12, "Assets Held for Sale," for further information.

(3) 
    These assets are primarily comprised of building improvements, computer software, hardware and equipment at Eversource Service.

The following table summarizes average remaining useful lives of depreciable assets:
 
As of December 31, 2017
(Years)
Eversource
 
CL&P
 
NSTAR Electric
 
PSNH
Distribution
34.6
 
35.8

 
31.7

 
31.3

Transmission
40.9
 
37.2

 
44.7

 
43.5

Water
32.0
 
—

 
—

 
—

Solar
25.0
 
—

 
25.0

 
—

Other
12.7
 
—

 
—

 
—

The depreciation rates for the various classes of utility property, plant and equipment aggregate to composite rates as follows:
(Percent)
2017
 
2016
 
2015
Eversource
3.0
%
 
3.0
%
 
2.9
%
CL&P
2.8
%
 
2.7
%
 
2.7
%
NSTAR Electric
2.9
%
 
2.9
%
 
2.9
%
PSNH
3.1
%
 
3.1
%
 
3.2
%