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PROPERTY, PLANT AND EQUIPMENT AND ACCUMULATED DEPRECIATION
 12 Months Ended
Dec. 31, 2016
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 overhead and AFUDC for regulated property.  The cost of repairs and maintenance, including planned major maintenance activities, is charged to Operations and Maintenance expense as incurred.  

The following tables summarize the investments in utility property, plant and equipment by asset category:
Eversource
As of December 31,
(Millions of Dollars)
2016
 
2015
Distribution - Electric
$
13,716.9

 
$
13,054.8

Distribution - Natural Gas
3,010.4

 
2,727.2

Transmission - Electric
8,517.4

 
7,691.9

Generation
1,224.2

 
1,194.1

Electric and Natural Gas Utility
26,468.9

 
24,668.0

Other (1)
591.6

 
558.6

Property, Plant and Equipment, Gross
27,060.5

 
25,226.6

Less:  Accumulated Depreciation
 
 
 
Electric and Natural Gas Utility    
(6,480.4
)
 
(6,141.1
)
Other
(242.0
)
 
(255.6
)
Total Accumulated Depreciation
(6,722.4
)
 
(6,396.7
)
Property, Plant and Equipment, Net
20,338.1

 
18,829.9

Construction Work in Progress
1,012.4

 
1,062.5

Total Property, Plant and Equipment, Net
$
21,350.5

 
$
19,892.4


(1) These assets are primarily comprised of building improvements, computer software, hardware and equipment at Eversource Service.
 
As of December 31,
 
2016
 
2015
(Millions of Dollars)
CL&P
 
NSTAR
Electric
 
PSNH
 
WMECO
 
CL&P
 
NSTAR
Electric
 
PSNH
 
WMECO
Distribution
$
5,562.9

 
$
5,402.3

 
$
1,949.8

 
$
841.9

 
$
5,377.2

 
$
5,100.5

 
$
1,804.8

 
$
812.3

Transmission
3,912.9

 
2,435.8

 
1,059.3

 
1,061.1

 
3,618.0

 
2,131.3

 
928.2

 
964.9

Generation
—

 
—

 
1,188.2

 
36.0

 
—

 
—

 
1,158.1

 
36.0

Property, Plant and Equipment, Gross
9,475.8

 
7,838.1

 
4,197.3

 
1,939.0

 
8,995.2

 
7,231.8

 
3,891.1

 
1,813.2

Less:  Accumulated Depreciation
(2,082.4
)
 
(2,025.4
)
 
(1,254.7
)
 
(338.8
)
 
(2,041.9
)
 
(1,886.8
)
 
(1,171.0
)
 
(307.0
)
Property, Plant and Equipment, Net
7,393.4

 
5,812.7

 
2,942.6

 
1,600.2

 
6,953.3

 
5,345.0

 
2,720.1

 
1,506.2

Construction Work in Progress
239.0

 
239.1

 
96.7

 
78.1

 
203.5

 
310.5

 
135.3

 
69.1

Total Property, Plant and Equipment, Net
$
7,632.4

 
$
6,051.8

 
$
3,039.3

 
$
1,678.3

 
$
7,156.8

 
$
5,655.5

 
$
2,855.4

 
$
1,575.3



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).  The composite rates, which are subject to approval by the appropriate state regulatory agency, include a cost of removal component (other than PSNH Generation), 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)
2016
 
2015
 
2014
Eversource
3.0
%
 
2.9
%
 
3.0
%
CL&P
2.7
%
 
2.7
%
 
2.7
%
NSTAR Electric
3.0
%
 
3.0
%
 
3.0
%
PSNH
3.1
%
 
3.2
%
 
3.0
%
WMECO
2.7
%
 
2.7
%
 
3.3
%


The following table summarizes average remaining useful lives of depreciable assets:
 
As of December 31, 2016
(Years)
Eversource
 
CL&P
 
NSTAR Electric
 
PSNH
 
WMECO
Distribution
35.1
 
37.7

 
32.0

 
31.3

 
30.7

Transmission
41.5
 
38.0

 
43.8

 
43.5

 
49.7

Generation
29.0
 
—

 
—

 
29.1

 
25.0

Other
11.0
 
—

 
—

 
—

 
—